Hi

I am doing a project for a mechatronics subject in university and we have to design a logic circuit to drive a device forward for a certain period of time, wait for a period and then reverse..

i decided to use two 4-bit digital counters with a clock circuit from a 555 timer to effectively make an 8 bit counter, and then use logic gates to determine the specific states

everything works with that part of it and the states i have is forward, stop for double the time and then reverse again

now i need to use these logic signals to control the SN754410 in order to run the motor forwards and backwards.. and that is where i am having trouble..

i have attached a diagram of the circuit i did in tinycad

i should state first that i have absolutely no idea what i am doing, so i am sure hte way i have done it is horribly inefficient or completely wrong.. i have just been doing all this just by reading data sheets and connecting pins up on a breadboard..

my problem is that although i can get a signal out of the logic ICs i am not getting anything out of the driver.. i am connecting logic high for forward to 1A and logic high for backwards to 2A and then the motor to 1Y and 2Y respectively, is this the right configuration?

i was worried that because i have used so many LEDs and resistors connected to ground that it may have dropped the voltage to below TTL levels, could this happen? ultimately i probably wont have all the LEDs in the circuit, but without them its hard to know if youre doing it all properly or not.. if i were to take them out could this help?

i am a bit confused with the whole thing really..

any help would be greatly appreciated

cheers
gus

 

In the diagram, the signal to the 754410 are shown as connected between the leds and resistors. They should come straight from the outputs of the logic gates.

You also need a LOT of power decoupling and a proper 5V regulator - you have no chance of running logic gates that drive LEDs using a resistor divider, and you seem to have other 74LS Series parts running directly from the 9V supply??

 

thanks for your quick response..

i wasnt sure about running the binary counters direct from the 9V supply, but it seemed to work, but i will get a regulator and use that.. probably easier that way..

is the 7805 good to use?

if i run the signal straight from the gates to the 754410 will that be stronger?

is there any way i can put an LED in so i can know which signal is being sent to the driver? can i just put one in series or does it have to be connected to ground?

sorry for all the beginner questions!

cheers
gus

 

A 7805 is fine, just add the correct input and output capacitors to prevent it oscillating.

You can leave the LEDs and resistors connected to the gates as they are, just take the logic signals direct from the gates as well.