In addition, drift rates are far superior to vacuum tube circuits allowing a 0.5 volt full scale range which is impractical with most vacuum tubes. The low-leakage, low-noise 2N4340 is an ideal device for this application.

Current meter ranges from 100 pA to 3 mA full scale. Voltage across input is 100 µV at lower ranges rising to 3 mV at 3 mA. The buffers on the op amp are to remove ambiguity with high-current overload. The output can also drive a DVM or a-DPM.

Parts list :

Parts list :
R1 : 20K
R2 : 60K
R3 : 30K
R4 : 1M
R5 : 1G
R6 : 10K
R7 : 1K Variable
R8, R9 : 2K
R10 : 6.65K
R11 : 2K8
R12 3.32K
R13 : 1K
R12 0.8 ohm
C1 : 30pF
D1 : LM385 1,2V
D2,D3 : 1N457
Q1 : 2N2484
Q2 : 2N2219
Q3 : 2N2905
A1 : LM11
M1 : 100uF

This zener tester based on famous 741 operational amplifier. RV1 can be calibrated in volts, so that when LED 1 just lights, the voltage on pins 2 and 3 are nearly equal. Hence, the zener voltage can be read directly from the setting of RV1. The supply need only be as high a value as the zener itself For a more accurate measurement, a precision pot could be added and calibrated.

Zener tester parts  list :
R1 : 4K7
RV1 : 10 K linier variable resistor
Led
IC1 :  LS741

Diode tester parts list :
D1, D2 : HEP R0052
LP1, LP2 : GE 4B lamp
X1 : 120V tp 6.3V, transformer, Lafayette 33P80508

Do you want to connect a traditional PC monitor on the VGA output of the MAC (Apple)? Yes you can. It is not the same connector, but this can be done with simple adaptation. No need to add the electronic components to this MAC VGA adapter. It’s just changing the connection between the cable and connectors.

The two connectors are D-Sub 15 points, but the next type of monitor is high density, with three rows of five points instead of two rows of eight and seven points for South-D 15 classic. Note that the vertical sync terminal is not used VertSync side monitor, only the horizontal sync HorzSync terminal is used. The latter receives the composite sync C. Sync from the MAC. The rest of the wiring does nothing special: the three terminals of the component video RGB (Red-Green-Blue, RGB for Red-Green-Blue) are in direct correspondence with their respective mass. Don’t know what the limits are Idx.

The Rain Alarm circuit applies 4 NAND gates of the 4011 IC. In each individual oscillator, while a single gate is configured a straightforward inverter, some other has one input that will act as a control input. Oscillator action is inhibited if this enter is held low. The first oscillator (IC1a and also IC2b) has this kind of input tied low through a high value resistor (R1) which acts as a sensitivity control. Thus this oscillator will be disabled until the control input is taken high. Any moisture bridging the sensor track will so enable the output which is a square wave at about 10 Hz. This in turn will gate on and off the 500 Hz oscillator formed by IC1c and IC1d. This latter oscillator drives the loudspeaker via R6, the Darlington pair formed by Q1 and Q2, and resistor R7.

Hardware Specifications:
- Measuring voltage: 100-330V AC, 50Hz;
- The interval between measurements of 0.5 sec. (Updated all the 6 values)
- Power supply module receive and display: 7-25V DC;
- Breakdown Voltage-isolated modules: 5.0kV;
- The maximum measuring error: ± 1,5%.

Analog-digital conversion is performed by the ADC is integrated into the MC ATmega8. To measure the rms ac voltage peak detection algorithm is implemented sine wave and its subsequent multiplication by the amplitude coefficient of a sine wave.
Power measuring unit and the transfer is made ​​through the transformerless power supply from the first channel of the measured voltage. When the voltage on the channel below the 90V module is disabled. HL1 LED is used to indicate the transfer of information receiver module.

Module is powered by the reception and display of an external DC voltage 7-25V.
In the normal mode on all the indicators show values ​​of the measured voltage corresponding to each channel. In the absence of packet from the transmitter for more than 2 renewal periods (about 1.4 sec.) On all indicators displays the word “Err”, that indicates a breach of the communication channel, or malfunction of the transmitter.Display returns to normal after the next transfer. Reducing the voltage on any channel except the first, below 100 V leads to the display dashes “—” on the appropriate indicator, the other channels are displayed as normal.

In Multi-channel remote voltmeter design, measure the AC mains only, but by making minimal changes to the software portion of IC transmitter module, as well as changing the voltage divider resistors R5-R10 and R11-R16, may be measured and a constant voltage to all or several separate channels.

MCU firmware, printed circuit boards in the GIF format and LAY (SprintLayout), as well as photos of the finished device, you can download here (430 KB) .

This simple LED circuit makes the  LED effect as in Knight Rider LED car. The chain of nine high-brightness LEDs are constantly running from left to right and from right to left. You can use red LEDs, and to attract additional attention to the front – white LEDs.

All types of CMOS chips are used, so it can be powered by a 9V battery PP3, which is enough for a very long time, since the current consumption of the Knight Rider LED circuit quite small.

How its work :
To IC4, C1, R1 and R2 made ​​a pulse generator, which come at terminals 14 of both counters IC2 and IC3.
IC1 – this is a trigger that is used to switch counters IC2 IC3 pin or permit 13.
IC7a valve determines which of the counters have appeared “1″ at the output of Q9 (output 11), ie, which of the counters count up to a maximum value.
IC5, IC6 and protect IC7a output of the counter IC2 and IC3, using the gates, “OR” that feed the anodes of LEDs 1 … 9.

Parts list :
R1,R2 : 10 k ¼
R3 : 470 ohm ¼
C1 : 6.8 uF/16v
IC1 : 4027 one flip-flop
IC2 and IC3 : 4017 two decimal counter
IC4 : 555 timer
IC5, IC6 and IC7 : 4071 three chips gates, “OR”
9 V battery size
high-brightness LEDs
Housing for Knight Rider LED circuit

The proposed diode tester and transistor tester circuit above are very simple and quite universal. Allows you to quickly test transistors, diodes, or ping circuit.

If the transistor broken, the corresponding LED will blink, indicating the structure of the transistor audited. Diodes which will be verified connected to “E” and “K”. If the diode working properly and the anode connected to the “E”, LED “A” will flash. LED “K” will flash, if the diode cathode connected to the “E”. When a diode broken or absent both LEDs flashing or not lit. The same probes are used for continuity checking circuits, or electrolytic capacitors.

The diode tester and transistor tester schematic requires a +5 Volt supply voltages, the probe can be connected to the computer’s power supply (red cable 5 volts, -5 volts black).

The basis of the device connected to the serial port serves as a digital thermometer DS18B20, by Dallas Semiconductor.

Documentation for the DS-18B20 can be found here: DS18B20.pdf , Assembly instructions thermometer.