Spot the Difference?

[circuitfish]

Hi all,

I've built a circuit which is a heat controlled stepper motor. It was all working fine but when the motor was off it still used some current. To stop this I used a 4081 chip to And the data latch outputs with my Schmitt trigger output as shown below. (I've used two 4013 chips for my data latches).

Trouble is the circuit doesn't work and seems lifeless. Can anyone see what I've done wrong? The yellow wires are the new section. I've checked the circuit voltage and on a 4.5v power supply, the voltmeter reads far less than this which seems odd.

Thanks,
**broken link removed**

**broken link removed**

 

[circuitfish]

Anyone? Please help - it would be much appreciated.

 

[mneary]

Without pin numbers on your "schematic" it's going to take a loooong time to verify your construction.

How did you wire it (accurately) with no pin numbers?

 

[MrAl]

Hi,

Yes some pin numbers would be nice

My additional suggestion is that you look at the output of the logic gates and make sure you have the right pattern. Also check the output of the driver to make sure that
has the right pattern. In the process you should be able to find out what went wrong.

 

[MRCecil]

Your second problem noted my be in the bussed signal on the AND inputs (yellow wires). Does that pulse have the same duration as the latch signals or is it of a much shorter duration? Try taking that line to Vdd and note the change if any.

Your initial problem may be both enables of the bridge you have set at Vss. I would suggest you return to your original configuration that was working, and look at the datasheet's truth table. Keeping the enables high with the latches in steady state should be the cause of the motor current at issue. With the outputs at high Z, there won't be any output current.

 

[Boncuk]

The L293 has two Enable pins (1,2E=pin1, 3,4E=pin9) When 'E' is high the outputs follow the control inputs, when 'E' is low the outputs go to high-z state.

I'm missing nets for the Enables.