S1Ngle-Ic Logic Probe


Posted on Nov 14, 2012    8388

This logic probe uses a CD4009 CMOS hex inverter. The characteristic high-input impedance of CMOS gives the advantage


S1Ngle-Ic Logic Probe
Click here to download the full size of the above Circuit.

of not loading the circuit being tested. Because the output of the inverters is not specified at either a high or low level with a floating input, an input-bias network produces lows at both input inverter pairs if the input is open or at less than 2 V. Resistor R3 holds the input of inverter 3 low which makes the output of inverters 4 and 5 low and will not permit LED 2 to light. At the same time, Rl holds the inputs of inverters 1 and 2 high so that their output is low and LED 1 will not light. If the probe input is touched to a logic low, the output of inverter 3 is held high by R3 and inverter 1 and 2 are brought low, which causes their outputs to go high and turns on LED 1. With no input, both LEDs should be off.




Leave Comment

characters left:

New Circuits

.


Top