Telephone status indicator with LED
This will monitor telephone status without loading the telephone line, this way if you have two phones in parallel you will know if one of them is busy. Connect the two ends of circuit...
Category: Discrete-Circuits
Flashing Mains Neon Lamp
Here is a Neon Flasher circuit (untested) for a user request at Circuits FAQ. This can be built into a switchboard or a gadget for indicating Live Power. D1-C1 form a simple half-wave rectifier,...
Ohmmeter – Simple Resistance Measurement
Measurement of resistor values in circuit configurations are required to be made often, as these might have changed in value due to various tolerance ranges, and hence could be the cause of faults. Likewise...
Voltage Doubler with Diodes
This is a Simple Voltage Doubler to boost 3V battery voltage to power some low-power 5V circuits. In needs a Clock input with high fan-out. You can use the 74HCT540 in parallel. Work with...
Simple Water operated relay
This was done in my early days, i have upgraded it, it ought to work, reduce the number of transistors to make it less sensitive, also a lower value in place of 10M will...
FET Current Source and MOSFET
This is a constant current source using a FET. This is the most simple replacement to series resistor to limit current. The N-Channel FET BF256C can give 15mA current. Simple Methods Before you get...
Voltage Doublers and Multipliers
Voltage multipliers are used to obtain low current high voltage, from an existing AC Source. Step up transformers can be used, but the insulation problems and care that has to be taken for HV...
Constant Current Source LED Drive
This is a Constant Current Source LED Driver, When the LED driver Upper-NPN is driven by a voltage thru 4.7K the LED lights up. Assume that the Lower-NPN at bottom is absent. The current...
