Digital Speed Controller with Reverse

I personally have not built any speed controllers with reverse, but I have been asked if the digital speed control described above could be modified to have the reverse function.  The answer is this design.  Most of the circuit is identical with the speed controller without reverse, but there are some important changes.  One of the changes being that another bit was needed to indicate direction.  This leaves 6 bits to encode the pulse width.  With 6 bits we have 64 steps in the forward direction and 64 steps in the reverse direction.  The resolution of 64 steps is still very good.

The change is reflected in the clocking arrangements of the 40103 down-counter, that must be fed with a lower rate counting clock.  This does not affect the output rate of the PWM wave train.  In fact the range of possible output rates has now been expanded (if you prefer to use the higher rates).  What is important is to note that the connections to some pins are changed and if you have the pcb of the circuit without reverse, you need to modify it accordingly and not simply add the new electronics.

The additional NAND gates are used to provide to correct behaviour of the PWM with stick travel.  This means that with the stick full down, the output is high speed.  The speed reduces towards zero as the stick is moved towards the middle.  Then the speed goes up again as the stick is moved towards the fully up position.

The direction indication is obtained from Q7 of the 590.  In the circuit, this signal is shown driving a relay.  The relay contacts would switch over the connections to the motor.  The relay circuit is just an example.  What you connect the reverse signal to, depends on what the power chopper actually requires to perform the reverse function.

Last modified 25 May 2000