EPM3064ATC100-10 low–cost, high–performance device Altera MAX architecture

The EPM3064ATC100-10 is a low–cost, high–performance device based on the Altera MAX architecture. Fabricated with advanced CMOS technology, the EEPROM–based MAX 3000A devices operate with a 3.3-V supply voltage and provide 600 to 10,000 usable gates, ISP, pin-to-pin delays as fast as 4.5 ns, and counter speeds of up to 227.3 MHz. The EPM3064ATC100-10 in the –4, –5, –6, –7, and –10 speed grades are compatible with the timing requirements of the PCI Special Interest Group (PCI SIG).

EPM3064ATC100-10 absolute maximum ratings: (1)VCC Supply voltage With respect to ground: –0.5 to 4.6 V; (2)VI DC input voltage: –2.0 to 5.75 V; (3)IOUT DC output current, per pin: –25 to 25 mA; (4)TSTG Storage temperature No bias : –65 to 150 ℃; (5)TA Ambient temperature Under bias: –65 to 135 ℃; (6)TJ Junction temperature PQFP and TQFP packages, under bias: 135 ℃.

EPM3064ATC100-10 features: (1)High performance, low cost CMOS EEPROM.based programmable logic devices (PLDs) built on a MAXR architecture; (2)3.3-V in-system programmability (ISP) through the built in IEEE Std. 1149.1 Joint Test Action Group (JTAG) interface with advanced pin-locking capability; (3)Built in boundary-scan test (BST) circuitry compliant with IEEE Std 1149.1-1990; (4)High–density PLDs ranging from 600 to 10,000 usable gates; (5)4.5–ns pin–to–pin logic delays with counter frequencies of up to 227.3 MHz; (6)MultiVoltTM I/O interface enabling the device core to run at 3.3 V, while I/O pins are compatible with 5.0–V, 3.3–V, and 2.5–V logic levels; (7)Pin counts ranging from 44 to 256 in a variety of thin quad flat pack (TQFP), plastic quad flat pack (PQFP), plastic J–lead chip carrier (PLCC), and FineLine BGATM packages.




CA3140E        DS2118MB           74HC04D            4N25            UC2854DW
TL084CN         TL082CP           PCI9052          OPA2277U         MC145407DW
LXT905PC       MAX1631EAI          LM224J           LT1260CS          LM35DM
MAX890LESA      LM331N           MC145406DW          LF353N            LM1881N

MAX3243CAI RS-232 Transceiver IC Maxim

The MAX3243CAI is a 1μA Supply-Current, True +3V to +5.5V RS-232 Transceiver with AutoShutdown. The MAX3243CAI achieves 1μA supply current with Maxim revolutionary AutoShutdown feature. When the MAX3243CAI does not sense a valid signal level on its receiver inputs, the on-board power supply and drivers shut down. This occurs if the RS-232 cable is disconnected or if the transmitters of the connected peripheral are turned off. The applications of the MAX3243CAI include Notebook, Subnotebook, and Palmtop Computers, Battery-Powered Equipment, Hand-Held Equipment, Peripherals and Printers.

MC34118DW IR2112S L6219DS MAX706CSA ADM202EARN AD826AR EPM7128SLC84-15
ATMEGA8L-8AU AD9883AKST-110 EPM3032ATC44-10 AD9884AKS-140 DG412DY FDS4435
SP3243ECA SAA7111AHZ SAA7118E MAX1644EAE IR2101S LM317 LF347N

LM358N - DEW Sensor

                                  LM358N

The following schematic shows a simple DEW sensor circuit diagram using LM258N IC. As the humidity around the circuit goes up, the resistance in the DEW sensor increases. When the resistance reaches a pre-specified level, the circuitry displays a warning message, and shuts down the external device

Under normal conditions, resistance of the dew sensor is low (1 kilo-ohm or so) and thus the voltage at its non-inverting terminal (pin 3) is low compared to that at its inverting input (pin 2) terminal. The corresponding output of the comparator (at pin 1) is accordingly low and thus nothing happens in the circuit. When humidity exceeds 80 per cent, the sensor resistance increases rapidly. As a result, the non-inverting pin becomes more positive than the inverting pin. This pushes up the output of IC1 to a high level. As a consequence, the LED inside the opto-coupler is energised. At the same time LED1 provides a visual indication. The opto-coupler can be suitably interfaced to any electronic device for switching purpose. Circuit comprising diode D2, resistors R5 and R6 and capacitor C1 forms a low-voltage, low-current power supply unit. This simple arrangement obviates the requirement for a bulky and expensive step-down transformer.






4N35 PC16552DV LM393M IR2110S LM386N-1 DS26C31TM UC3854DW
OPA2134ua OPA627AU MAX232ACSE MAX485CSA BAT54C

EPM240T100C5N PCF8574AT PCM1725U LM311N MAX1711EEG L2800-38
L6219 DG444DY

Dual Differential Comparator LM393

These devices consist of two independent voltage Comparators that are designed to operate from a single power supply over a wide range of voltages. Operation from dual supplies also is possible as long as the difference between the two supplies is 2 V to 36 V, and VCC is at least 1.5 V more positive than the input common-mode voltage. Current drain is independent of the supply voltage. The outputs CAN be connected to other open-collector outputs to achieve wired-AND relationships. The LM193 is characterized for operation from 55C to 125C. The LM293 and LM293A are characterized for operation from 25C to 85C. The LM393 and LM393A are characterized for operation from 0C to 70C. The LM2903 is characterized for operation from 40C to 125C.

MAX232CWE

LM324N

LM393

MAX232CPE

Arduino and DS18B20 1-wire digital thermometer

Finally got this DS18B20 working. Actually three of them. And in two modes. Parasite power mode and main mode.
A 4.7K ohm resistor is the key.

Starting with the main mode, three wires are needed, as this sensor has three pins.
Data sheet is here : http://www.hqew.net/product-data/DS18B20

Connection is almost simple.
Pin 1 to Arduino ground
Pin 2 to Arduino digital input
Pin 3 to Arduino 5V
And a 4.7K resistor between pin 2 and pin 3

Works with three wires, as seen on the following illustration.

Parasite mode eliminates one wire.
Pin 1 to Arduino ground
Pin 2 to Arduino digital input
Pin 3 to Arduino ground (same as pin 1)
And a 4.7K resistor from pin 2 to 5V

Maybe following illustration helps.

Of course multiple DS18B20-s or different one wire devices can connected together like so:

Here comes the beauty of using digital thermometers. One pin on Arduino can be used for multiple devices, working together over one wire. Much like ethernet actually. Each device has its own unique address.
Second, a two wire cable can be used. Those are usually much easier to find than three wire cables. Also digital 1-wire thermometers work on longer cables. A simple test is cable-length-for-lm35-and-ds18b20.

Some words of caution:
No pins on DS18B20 should be left unconnected. Sometimes it works this way, sometimes it does not.
If using one should avoid mixing main mode and parasite mode thermometers on the same pin. Sometimes it works, sometimes it does not.

DS18B20 can also be installed outside. Some kind of protection is advisable.  I had one sensor outside, minimum temperature about -30° C, maximum about +35° C, protected like this. No problems so far.

Working with three DS18B20 thermometers for a year now – sometimes those thermometers do not get initialized correctly. Specially after power fluctuations. Hard reset helps in that case.



A1015         CP2102          DS18B20             AD620

Simple power supply ripple rejection for battery systems MMBT3904

Many amplifiers, including integrated devices, are afflicted with undesired, implicit input terminals in their power connections. Due to less than perfect power-supply rejection, these implicit terminals admit noise into the signal that the amplifier will magnify. Thus, a clean supply is essential for amplifiers.

But a regulated supply, even one using a low-dropout regulator (LDO), can create problems in a battery-based amplifier design. If the selected regulation voltage is close to the fresh battery voltage, the LDO will quickly drop out as the battery discharges, eliminating the noise protection. If the regulation voltage is far below the fresh battery voltage, the design sacrifices the amplifier’s output voltage swing and wastes power until the battery voltage drops close to the LDO regulation voltage.

Fortunately, most audio amplifiers can readily operate with an unregulated supply because they do not need to provide dc precision. Unregulated supplies are especially useful in battery-powered designs that seek to use the battery fully because the circuits will continue to operate until the battery is quite discharged. The unregulated supply must be clean, however, and of sufficiently low impedance to avoid injecting noise and inducing inter-stage coupling that might cause instability.

A good way to clean an unregulated supply is to use the so-called “ripple-eater.” The ripple-eater’s output voltage tracks slightly below its input voltage and continues to operate as the input drops to a fairly low voltage. The ripple-eater also provides a low output impedance most of the way down.

This ability to track declining input voltage can be very useful when the power source is a non-rechargeable battery. It may not be good, however, for battery systems that can be harmed by deep discharge.

One well-known ripple-eater design that has been popular among audio enthusiasts is available in kit form. That design, though, is relatively complex and operates by bucking the ripple. The simple ripple-eater shown here (Fig. 1) is far simpler and offers about 40 dB of low-power cleaning at audio frequencies (Fig. 2), making it useful for such functions as pre-amplifiers.

The design simply comprises a filter buffered by a follower. A voltage divider (R1 and R2) provides headroom for subsequent regulation. A low-pass filter (R3 and C1) provides a clean voltage that an emitter-follower (Q1 and R4) buffers, adding one diode-drop of offset. A pass transistor (Q3) and feedback amplifier (Q2) provide gain and cancel the diode drop of Q1.

This circuit has sufficient gain to require compensation, which R6 and C2 provide. The voltages at the base of Q1 and at the output are essentially equal, so the transistors form a fed-back follower.

The ratio of R1 and R2 should be chosen to set the ripple-eater’s output far enough below the input so the output is below any troughs in the input voltage. Otherwise the circuit will “drop out” like any other regulator.

If more power is needed than the simple ripple-eater can provide, using a composite transistor in the feedback will provide more gain (Fig. 3). The higher-power version adds Q4 and R7 to increase gain beyond what Q2 alone provides, and the diodes (D1 to D3) increase headroom for the composite transistor’s operation. The result has greater ripple rejection in the audio band (Fig. 4) but loses effectiveness in the high-frequency band.

The high-frequency performance of the simple ripple-eater is another advantage this circuit has over LDO regulation. Many LDOs, especially those with MOSFET pass transistors, exhibit poor power-supply rejection (PSR) at high frequencies.

While the transistors shown are sufficient for audio operation, with high-frequency transistors such as the MMBT3904 and MMBT3908 the circuit of Figure 1 has proven effective where rejection up to a few megahertz was needed. The MBTH10 and MBTH81 can be used for even higher frequency rejection.



1N5819      ATMEGA64           MMBT3904          FR107

ULN2803A HIGH-VOLTAGE, HIGH-CURRENT DARLINGTON ARRAYS

The circuit diagram of this programmable sequencer could be applied in a number of timing uses. Prior to the start of each interval, an audible tone is generated, and a seven-segment LED display shows the interval number. Prior to the end of that inerval, the buzzer sounds again. IC1 is a 2240 timer/counter device that clocks up to 256 periods, the durations of which are determined by resistor R1 and capacitor C1. The 2240 has its RESET and TRIGGER pins (10 and 11) wired via a push switch S1.The timer is used to operate a memory chip, IC2. The first 8 addressed bits are used by the timer/counter to step through the 256 steps available for each program. The other 6 bits are selected by an external switch network S2 to S7 which permits up to 26 programs, each of 256 steps. The 27C64 has eight outputs, which was enough for a single-digit LED display plus a piezo buzzer.

The ULN2803A is a high-voltage, high-current Darlington transistor array. The device consists of eight npn Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes for switching inductive loads. The collector-current rating of each Darlington pair is 500 mA. The Darlington pairs may be connected in parallel for higher current capability.

Applications include relay drivers, hammer drivers, lamp drivers, display drivers (LED and gas discharge), line drivers, and logic buffers. The ULN2803A has a 2.7-kΩ series base resistor for each Darlington pair for operation directly with TTL or 5-V CMOS devices.


 HT1621        TEA2025B           ULN2803A         IRFP250N

An electronic ballast model 234SLESW designed SS8050

This is the schematic of an electronic ballast model 234SLESW designed for running a pair of 4 foot T8 or T12 fluorescent bulbs.  It claims to have an Energy Star rating when used with F32T8 bulbs.  I picked one of these out of a dumpster and it was broken so I had to draw up a schematic.  I figured I'd share it with you.  It should be fairly easy to construct if you needed a light, efficient, flicker free ballast for your shop or garage or heck, even your living room!


WARNING: This circuit is AC line powered and contains voltages and currents which can KILL if you are not careful. Charged capacitors will SURPRISE YOU! They can hold a lethal charge for hours! If you don't know much about working with line (and higher) voltages or if you aren't crazy (like me) then DO NOT attempt to construct this circuit. I CANNOT BE RESPONSIBLE if you electrocute yourself to death! That said, let's have some fun!

Parts List
R1, R6 470K Non-Flameproof
R2 22R
R3, R5 1R
R4 30R
R7, R9 30R 1/4W
R8, R10 22R
R11 47R 1/4W

CO1, C7, C8 470n, 250V
C1, C4, C5 100n 63V
C2, C3 47u, 250V
C6 2n2
C9 - 12 33n, 630V
C14 3n3, 2KV Ceramic disc

L1 See Notes
L2 See Notes
L3 See Notes
T1 See Notes

D1 - D5 1N4007

Q1, Q2 PHE13005
Q3, Q4 SS8050

DIAC 32V, DB3

RV 270V 10% Zinc Oxide Varistor ZOV-07D271K

F1 2.5A

All resistors 1/2 Watt and flameproof unless otherwise specified.  All capacitors polyester unless otherwise specified.

Pump Controller For Solar Hot Water System LM335Z

This circuit optimises the operation of a solar hot water system. When the water in the solar collector is hotter than the storage tank, the pump runs. The circuit comprises two LM335Z temperature sensors, a comparator and Mosfet. Sensor 1 connects to the solar collector panel while Sensor 2 connects to the hot water panel. Each sensor includes a trimpot to allow adjustment of the output level. In practice, VR1 and VR2 are adjusted so that both Sensor 1 and Sensor 2 have the same output voltage when they are at the same temperature. The Sensor outputs are monitored using comparator IC1.

When Sensor 1 produces a higher voltage than Sensor 2, which means that sensor 1 is at a higher temperature, pin 1 of IC1 goes high and drives the gate of Mosfet Q1. This in turn drives the pump motor. IC1 includes hysteresis so that the output does not oscillate when both sensors are producing a similar voltage. Hysteresis comprises the 1MO feedback resistor between output pin 1 and non-inverting input pin 3 and the input 1kO resistor. This provides a nominal 12mV hysteresis so that voltage at Sensor 1 or Sensor 2 must differ by 12mV for changes in the comparator output to occur.

Since the outputs of Sensor 1 and Sensor 2 change by about 10mV/°C, we could say that there is a degree of hysteresis in the comparator. Note that IC1 is a dual comparator with the second unit unused. Its inputs are tied to ground and pin 2 of IC1 respectively. This sets the pin 7 output high. Since the output is an open collector, it will be at a high impedance. Mosfet Q1 is rated at 60A and 60V and is suitable for driving inductive loads due to its avalanche suppression capability. This clamps any inductively induced voltages exceeding the voltage rating of the Mosfet.

The sensors are adjusted initially with both measuring the same temperature. This can be done at room temperature; adjust the trimpots so that the voltage between ground and the positive terminal reads the same for both sensors. If you wish, the sensors can be set to 10mV/°C change with the output referred to the Kelvin scale which is 273K at 0°C. So at 25°C, the sensor output should be set to (273 + 25 = 298) x 10mV or 2.98V.



Note:

The sensors will produce incorrect outputs if their leads are exposed to moisture and they should be protected with some neutral cure silicone sealant. The sensors can be mounted by clamping them directly to the outside surface of the solar collector and on an uninsulated section of the storage tank. The thermostat housing is usually a good position on the storage tank.


LM335Z circuit

LAN RJ45 Cable Connection Tester

Here's a very simple, but practical circuit, which is used to check the type of LAN cables (straight or cross) as well as possible faults. So we use a unit that has 8 outputs, each one of which produces a pulse successivly. Only one output can be high at any time. Then we use two rj45 connectors and we apply the pulses to the 8 pins of one connector (A) wnd we connect LEDs at the pins of the other connector (B). If we connect a straight LAN cable, we notice that the LEDs glow one by one successively. If a wire is broken, the coresponding LED will not glow. Just watch the LEDs. If we connect a cross wire, then the order of LEDs glowing changes to 1,2,7,4,5,8,3,6. So we can laber the LEDs in that order, so that we can watch easily.
If both ends of the cable are not close enough to be pluged onto the curcuit, we can use an remote board, which has only one rj-45 connector and 8 LEDs. Then plug one end of the cable to connector A on main board and connect the other end to the remote unit. Notice that no common wire is needed for the remote unit.

I have included an alternative circuit instead of using classic ics, I use the AVR ATtiny2313, but any AVR controller can be easily adapted. See photo and diagram.



RJ45 Description

How to build Touch Activated Light Description SK34

The circuits below light a 20 watt lamp when the contacts are touched and the skin resistance is about 2 Megs or less. The circuit on the left uses a power MOSFET which turns on when the voltage between the source and gate is around 6 volts. The gate of the MOSFET draws no current so the voltage on the gate will be half the supply voltage or 6 volts when the resistance across the touch contacts is equal to the fixed resistance (2 Megs) between the source and gate.
The circuit on the right uses three bipolar transistors to accomplish the same result with the touch contact referenced to the negative or ground end of the supply. Since the base of a bipolar transistor draws current and the current gain is usually less than 200, three transistors are needed to raise the microamp current level through the touch contacts to a couple amps needed by the light. For additional current, the lamp could be replaced with a 12 volt relay and diode across the coil.

SK34 IC

Vertical Defl Ection Output Circuit With Bus System Support LA7840

The LA7840 is a vertical deflection output IC for high-definition TV and CRT Displays in systems that use a bus control system signal-processing IC. This IC CAN directly drive (including the DC component) the deflection yoke from the sawtooth wave output from the bus control system signal-processing IC. The color TV vertical deflection system adjustment function CAN be controlled from the bus system when this IC is used in conjunction with a SANYO LA768X or LA769XX series TV bus control system signal-processing IC. By Sanyo Semiconductor Corporation

Low Power Dual Operational Amplifier LM2904

The LM158 series consists of two independent, high gain, internally frequency compensated Operational Amplifiers LM2904 which were designed specifically to operate from a single power supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage.

Application areas include transducer Amplifiers dc Gain Blocks and all the conventional op amp circuits which now CAN be more easily implemented in single power supply systems. For example, the LM158 series CAN be directly operated off of the standard +5V power supply voltage which is used in digital systems and will easily provide the required Interface electronics without requiring the additional 15V power supplies.

The LM358 and LM2904 are available in a chip sized package (8-Bump micro SMD) using National's micro SMD package technology.

LM2904 pdf datasheet

Simplest FM Transmitter S8050

This is the simplest fm transmitter circuit you can ever find on internet,because so many “simple transmitters” (they call it simple but many of them don’t work!) on internet will not work as those circuits are designed poorly. i had built around 100s of transmitters in the past and most of them were built successfully, because the design is just cool and reliable. This circuit is for those who have built many fm transmitters without any sign of working!, so try this one and i am sure you can make it!.



An Fm transmitter is a circuit/device to transmit audio signals to an fm radio receiver through air (wirelessly). The input (audio)to an fm transmitter can be fed using a microphone or the output of your music player to be transmitted, and the signal which you transmit can be received using an FM radio, the advantages of FM TRANSMITTERS ARE many:

1.You may transmit audio to another room/floor of your house without using any wires!

2.You may transmit your own voice if you used an electret microphone in the circuit

3.You don’t need to build a receiver to receive the ransmitting audio as any standard fm radio can be used to receive your voice/audio and many..!



this circuit can transmit audio to a distance of around 50 meters if you used 2n3904 transistor and boost the supply voltage to 6V, and 1Km(1 kilometer) if used S8050 transistor with 9V supply!

Components you need

R1 – 47K resistor

R2 – 100 ohms resistor

C1 – 22n none polarised capacitor

C2 – 1n none polarised capacitor

C3 – 4.7pf none polarised capacitor

c4 – 22n none polarised capacitor

T1 – Transistor BC547(short range),2N3904(medium range,recommended),S8050(long range)

VC1 – 22pf Variable trimmer capacitor (trimcap)

L1 – Aircore inductor, 6turns on a 3mm dia former eg.Wind over a pen refill.

Antenna – a short length wire

3V battery (Use only battery)

Good quality pcb or veroboard. (breadboards may not work)

Testing
after building is done,power the circuit using a 3V battery and connect any audio source to “audio input” pin properly, set an fm radio minimum 3 meters away. Start tuning the radio and tuning the VC1 at the same time untill you receive the transmitting audio, if you can hear the audio then you are DONE!.

Notes

1.All components in the circuit is not intended to change their values

2.Using correct value components in the circuit is vital

3.If the transmitting audio is too loud and unclear, then add a 100K or 1 Mega ohm resistor across the audio input pin, the value of this resistor depends on how much powerful you audio signal is and should be selected untill you get a very clear voice.

SMART AC POWER STRIP LM358N

The schematic of the Smart Strip circuit is shown. The ac line input is connected directly to the 117-Vac line of a power strip. The voltage is rectified by diode D1 and filtered by capacitor C2. The load-sense lines are connected to the ac socket in the power strip that will contain the device that will be used to turn the others on. When the load sense device is turned on, current flows through R1, a 1-Ω, 10-W resistor. To limit the power in R1 to 5 W, therefore, amaximum load ofno more than 5 A should be connected to the load sense outlet. The resulting voltage drop across R1 is fed to one section of an LM358N op amp, IC1-a, through resistors R2 and R3. Zener diode D4 limits the supply for the op amp to 15 Vdc. The voltage drop across R1 could be very small if the device plugged into the load sense socket does not draw much current. To ensure that the circuit is sensitive enough to detect such small-load devices, the gain of IC1-a is set at 470 by resistors R2 and R4. Because the out-put IC1-a is halfway rectified, diode D2 and capacitor C3 are used to form a peak-hold circuit. As long as CB is charged to 0.7 V or more (when a powered-up load sense device is detected), transistor Q1 will be on, and relay RY1 will close. When those normally open contacts close, the hot line is connected to the "load-switched" sockets, effectively turning on any devices that are connected to those outlets. Diode D1, resistor R6, and capacitor C1 provide a dc supply for the 12-V coil of the relay; diode D3 acts as a clamping diode.

IR2110 based power stage circuit

I started to build up the Open-BLDC circuit on a breadboard. Then a problem occurred. The low side works as it should but the high side just did not. After several hours of trying and reading the data sheet of IR2110 I gave up and asked Federico again for help. After some time we found an application note AN-978 from International Rectifier. This explained everything. You need to select very carefully the Boot capacitor. This is the one between VB and VS pins of IR2110. It is providing the charge for the gate of the high side MOSFET when you turn it on.

For testing you can take a big capacitor, so that when you manually switch on the high side you see something happen. I took a 330uF capacitor and it is enough to turn the high side MOSFET on for about 30 seconds. Still you have to be careful because the capacitor only gets charged when the low side MOSFET is turned on. So after turning on the power the capacitor is not charged and you have to turn the low side MOSFET on first, then turn it off again and finally switch the high side on.

In the final design one should probably select the right bootstrap capacitor. The equation for calculating that value is described on page 6 of the International Rectifier application note AN-978.

You can probably get rid of the capacitor and the diode if you connect VCC directly to VB. The problem you get then is that when the current on VS gets higher then 12V you get a problem. But I may be mistaken. Correct me if I am wrong.

Conclusion: read the damn application notes and I still have problems with understanding the electrical engineer talk! 

I hope this helps someone. You can see my circuit for one half bridge attached to this post. And a picture of my breadboard.

I use the two LEDs to see what happens with the MOSFETs. They are glowing a little when both sides are off. The one connected to 12V is switching off when the high side is on and the one connected to GND switches off when the low side is on. I love LEDs!

projects/bench psu personal bench power supply mk1 LM2596

This Hackspace project aims to create simple, low cost, robust, and safe variable voltage power supplies for experimental use in projects. While we have good bench power supplies in the Hackspace it is often useful to have something personal and portable for you projects. It is hoped that the Personal Bench Power Supply will develop over a few iterations as we learn.

I have gone for a very basic specification for the Mk1 version to achieve an availability .
- Low cost £5 to £10
- No exposed mains voltage to builder or user
- Voltage range < 3 Volts to > 12 Volts variable
- Current up to 2A (not variable limited) Fuse protection
- 4mm screw binding post output
- Visual readout of voltage
- Laser cut or simple self build case
- Pocket size
Power Source To achieve the voltage range, current, and safety objectives; a laptop power supply is used. Usually these provide between 16 Volts and 19 Volts and adequate current). These are power supplies are usually very low cost or free.
The plan is to plug the laptop power supply into the variable regulator module. Panel mounted power jack sockets seem common in 2.1mm and 2.5mm pin, but not common in 1.5mm, so a laptop power supply with a 2.1 or 2.5 plug is preferred (need to look into long vs. short plugs)

Regulator Board
From the voltage range, current, and size perspective a switching regulator is most appropriate for the variable regulator. The disadvantage of switching regulators is their higher ripple voltage on the output especially at lower currents.
This is the switching regulator module I chose. The module is low cost at £1 each, and avoids having to make a PCB.

The boards come in a few different pcb layout but generally have the following circuit using the LM2596 regulator.

The TI/National WebBench power supply design too also supports the LM2596. Analysis of the above circuit with the design tool shows that the LM2596 will operate in discontinous mode at the currents we will supply, so ripple on the output may be an issue in some applications.

Voltmeter
The voltmeter is based on a ready built module costing around £1.70 each. It is a 3 digit red LED meter reading from 0 to 99.9V:


The schematic shows the voltmeter is based on an STM8 flash micro and is hackable in itself:

Note: the devices S1 and S2 are not switches, but 4 off 220R resistor array to limit LED current. The digit drive M4 is not used because it is only a 3 digit display.

Digital voltmeter using ICL7107

The circuit given here is of a very useful and accurate digital voltmeter with LED display using the ICL7107 from Intersil. The ICL7107 is a high performance, low power, 3.5 digit analog to digital converter. The IC includes internal circuitry for seven segment decoders, display drivers, reference voltage source and a clock. The power dissipation is less than 10mW and the display stability is very high.

The working of this electronic circuit is very simple. The voltage to be measured is converted into a digital equivalent by the ADC inside the IC and then this digital equivalent is decoded to the seven segment format and then displayed. The ADC used in ICL7107 is dual slope type ADC. The process taking place inside our ADC can be stated as follows. For a fixed period of time the voltage to be measured is integrated to obtain a ramp at the output of the integrator. Then a known reference voltage of opposite polarity is applied to the input of the integrator and allowed to ramp until the output of integrator becomes zero. The time taken for the negative slope to reach zero is measured in terms of the IC’s clock cycle and it will be proportional to the voltage under measurement. In simple words, the input voltage is compared to an internal reference voltage and the result is converted in a digital format.

The resistor R2 and C1 are used to set the frequency of IC’s internal clock. Capacitor C2 neutralizes the fluctuations in the internal reference voltage and increases the stability of the display.R4 controls the range of the voltmeter. Right most three displays are connected so that they can display all digits. The left most display is so connected that it can display only “1” and “-“.The pin5(representing the dot) is connected to ground only for the third display and its position needs to be changed when you change the range of the volt meter by altering R4. (R4=1.2K gives 0-20V range, R4=12K gives 0-200V range ).

An Arduino Compatible Using CP2102

Standard Arduino boards use FTDI’s FT232RL to interface with computer’s USB port. Since FT232R is just a USB to UART converter, it is possible to build an Arduino compatible USB interface using other USB to UART chips.

One such alternative is Silicon Labs‘ CP2102. I particularly like this USB to UART transceiver because very few extra components are required for it to work. As an added benefit, this chip is also cheaper than the ubiquitous FT232R. Of course, there are also a few trade offs. First of all, CP2102 does not provide a bit bang interface (the X3 pins on the Arduino board on the other hand can be used for bit bang operations, but the X3 pins are not soldered with header pins by default and thus for the average users no bit bang support should not be an issue). Secondly, CP2102 does not have the configurable general purpose I/O pins to drive the TX/RX LEDs. There are other minor differences as well (for instance the maximum transmission speed for FT232R is 3Mbps while CP2102 tops at 1Mbps. Both chips are more than adequate for the maximum 115,200 baud rate supported in Arduino environment), but they do not affect the performance in our application of interfacing with Arduino.

Here is the schematics for using CP2102 with ATmega328p (the circuit below is compatible with the Arduino IDE):