Author Options:

Problem with the HEF4008BP IC chip ?? Answered

i just bought a HEF4008BP 4 bit binary adder ic. I connected pin 16 to V+ and pin 8 and 9(Carry in pin ) to ground  and then set up a 8 way DIL switch with 10k and 1k pull down resistors to gnd and the switch  to the inputs of the adder.Then i connected the outputs of the adder to the positive of a 3mm led each separately  .The dil switches are all of but still all the led's light up once i connect the 9v battery . The chip can run off 5v-15v . Also there is no sign, name or logo of a manufacturer on the ic .Is this a fake ic or might i have possibly blown it or have i done something wrong .Please help me.



5 years ago

Your wiring diagram is Correct on all counts.
The adder, the switches, the transistors and the LEDs.

Even the values are correct,
The 12 ma LED current with a 680 ohm series resistors and dip_sw pull downs.

If you have a picture of the actual breadboard maybe I could spot something.

If you have a meter or even use one of your LED transistors with base 47K as a probe.
And do around verify the adder input voltage levels to see if the outputs follow the  truth table.

Did you buy only one 4008 ?


See if the output circuit works without the adder chip.
Check that the chip really IS connected, using a meter. breadboards are very unreliable.

current limiting resistors on LEDS ???

DRAW circuit.

no not current limiting resistors pull down resistors for the inputs not for the led ,anyway here is the circuit: