switch between two pwm sources

Thread Starter

mah

Joined Mar 15, 2010
393
I have two PWM sources to control mosfet gate driver. the first source is MCU which isn't connected all the time (when needed)(it is not on the pcb), the second is timer 555 which is connected just when i push the buttons (right or left)(manual control and it is on the pcb). I isolated the two sources with pnp transistors to connect the timer 555 when i push the buttons assuming that the MCU isn't connected. the output of the transistors is connected to AND gate. then when i connect the MCU to drive the circuit according to the code without pushing the buttons , it will be isolated from 555 timer.
do you have comments on this circuit?
 

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AlbertHall

Joined Jun 4, 2014
12,345
Very difficult to read that diagram, especially with that migraine inducing background.
Two things seem evident. There is no way for the uC to control the direction. The direction output has an LED direct to ground so the maximum voltage on direction about 1.5V which is probably not what you want.
 

NorthGuy

Joined Jun 28, 2014
611
You could replace the 555 with a little tiny MCU. Then you could get rid of your circuit as well as all the discrete components which you use with 555.
 

Thread Starter

mah

Joined Mar 15, 2010
393
I simulated the circuit in separate sheet and it works fine. here is the results of right and left switch but when i connect it in the main circuit it stopped and the error message attached
Is this circuit enough for isolation? will it work?
 

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