logic circuit to control a DC motor

Thread Starter

J7NF

Joined Mar 12, 2016
18
Here you go I figured it out in the end, probably worth checking of course :). Just required some feedback from the second JK and a different initial state. This will now follow your required state diagram. Bear in mind this uses momentary (push to make) and not latching switches and you still need to determine your resistor values for the pull ups and base resistor and what NPN would be appropriate. Not sure what voltage (or current draw) your motor is but these TTL ICs need a 5 volt regulated supply so if your supply is higher than that for you motor you can just put a 7805 regulator in for the logic. You might also want to consider a general power switch further upstream in the circuit just so the power to the logic etc. isn't always on, unless you want it to be of course :).

View attachment 102423
I try this circuit, it has one problem at state 1, is that when you connect the circuit, the motor turn on directly without pressing any button. how to solve this issue please
 

Marcus2012

Joined Feb 22, 2015
390
I try this circuit, it has one problem at state 1, is that when you connect the circuit, the motor turn on directly without pressing any button. how to solve this issue please
Unfortunately my diagram as it is won't work with a 7476 because that is positive edge triggered, has a preset function and as a result has slightly different states than the 7473.



 

Thread Starter

J7NF

Joined Mar 12, 2016
18
Unfortunately my diagram as it is won't work with a 7476 because that is positive edge triggered, has a preset function and as a result has slightly different states than the 7473.


Ah ok, because I have only the 7474 and the 7476, any idea how to do the circuit by using the 7474's or 7476's ?
 
Last edited:

Marcus2012

Joined Feb 22, 2015
390
Ah ok, because I have only the 7474 and the 7476, any idea how to do the circuit by using the 7474's or 7476's ?
Try it with the 7476 instead but hold the preset pins of each high at 5V permanently, see if that helps. It's definitely a 74xx76 and not a 74xx76A?
 

Marcus2012

Joined Feb 22, 2015
390
This has simplified it a little more and it works in sim with a 74HC76 on mine I think that has the same function table as the 7476 but there are a few variations on that IC.

motor control 1.png

FYI S is PR in this diagram
 
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