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Here is a easy to read ‘Analog’ Millivoltmeter. Just like the Moving Coil Voltmeter, but does not have that resolution. This gives a easy indication of process progress or parameter magnitude from a large distance. A bargraph is easy on decision making too, compared to a digital readout.
How this Works ? – The analog input in mV – millivolts is fed to R18, RC reduces Noise and the Zener Clamps protect. The LF353 FET Opamp offers High Impedance as a Non-Inverting Amplifier, which nullifies measurement burden, Remember the Moving coil voltmeter loads the measured circuit, causing sizable errors. Then they invented the Vacuum Tube Voltmeter to solve this issue. An FET voltmeter is near ideal, they ought to have inventing this first.
The Zeners and C3 Plastic cap should not leak, even if they do it should be in Pico Amps. Get quality stuff and do a neat job putting them together. To master this leakage and other aspects, try building an Electrometer with CA3140. Another Measurement challenge is uV Microvolt measurements, you will be faced with new glitches in connectors and PCB due to thermocouple effects and contact resistance. A soldered joint near a hot resistor will set up enough thermal gradients and create many thermocouples all over the board. Try to measure 1 Microohm with a 10 Amp pulse or 1 A DC. You will learn many things. Connectors have a craze for the Precious Metal, they act funny if they do not have enough Gold on em.
Once i observed, very low voltages or circuits with nominal voltages but very low currents, cannot break a near invisible layer between the plates of a good connector. A sub-micron coat of corrosion, dust or even some organic deposit, was forming a dielectric layer which was impervious to uV and pA. A good cleaning with a volatile organic solvent solved the problem but messed up other plastics nearby.
Millivolt Meter using a LM3914 LED Dot Display. – This circuit is a part of my Build a DMM or Digital Multi Meter
This is dual 555 multivibrator like power oscillator. This is my contraption and conception but couple of decades old. It appears to have errors. It worked but the document fixing after design worked, not done. This can be used to make a small inverter, for powering 230V gadgets of low power. The transformer is used in step-up mode. It may make a sound if the laminations are not of good quality. This circuit can be modified using 7555 and switching transistors like BD139 driving a Ferrite 100 kHz transformer to build a Fluorescent Lamp of 10W to 20W. From Schematics Read More …
This is a easy to build LED lamp circuit for Learning and building skills. This is the first draft schematic V 1.0. It will need improvements for Higher Power Lighting. From Schematics of delabs I will give a short summary, The LM317 here configured for around 6.4V DC. The Q3 BC547 limits the current, you can select R3 to suit, make it 1/2W. The Ni-Cd battery pack 1.2 * 4 will not get Over-Current or Over-Voltage due to this circuit. The IRF540 Mosfet or any other equivalent you have around, along with Q2 BC547 forms a current source for the Read More …
This is the standard configuration on how to Interface a uC like 8051 to PC RS232 with MAX232A. The UART or Serial port was not present in 8049/8749 chips which were the ancestors of 8051/8031. Pages of code were needed to make a software UART in MCS-48. The 8051 integrated the hardware UART and short commands made it tick. The most important innovation which made uC popular was the C in 80C31. C is for CMOS. This made the chip work cooler and work on even batteries and small power supplies. The 8749 and 8751 are the UV EPROM type Read More …
Mains Voltage Stabilizer Circuits These circuits were drawn for a person in Africa. See the thread here… stabilizer circuit. They were not tested by me, but are quite close to a practical design. Stabilizer Step up 230V AC 500VA This circuit is a design i did, not tested by me as yet. It can Stabilize Mains voltage to around +/- 10% . It can be used for both 110V AC or 220V AC inputs with modifications. The Output is 220V AC. There is an overload, under voltage and over voltage trip circuit. With some tweaks and modifications it might work. Read More …