Question about output switch

[mattallen37]

Okay, cool.

It uses MOSFETs. They are not variable; they use PWM from the motor port to control the "power level". They are either all the way on or all the way off.

[h-g-t]

Well, when they are all the way on they act as a relay, without an external power source. And when controlling a motor, they are, in effect, acting as a variable resistance.

[mattallen37]

...And when controlling a motor, they are, in effect, acting as a variable resistance.

There are PWM, not variable resistance. Either would indeed effect the speed of a motor, but PWM is better in many ways.

BTW, I have noticed that the Relay Driver outputs are either off 1 and 2, on 1 off 2, or on 1 and 2. There seems to be no way to only have 2 on. Have you noticed this?

[h-g-t]

I did say 'in effect'.

Behaviour in port A is different from the other ports and I have only tried port C, works fine there.

[mattallen37]

...Behaviour in port A is different from the other ports and I have only tried port C, works fine there.

The H-Bridge of port A is different than the one used for ports B and C, and uses opposite polarity. That causes issues with the gate signals of the MOSFETs, as they are inverted.

[h-g-t]

wow

[mattallen37]

I'm sorry if that was offensive. I meant it to be informative.

[h-g-t]

No apology necessary - I was just in a bad mood that night!

Although the driver can operate two motors at variable speeds but only in one direction, I think it should be possible to operate a single motor in both directions using a latching double pole relay.

This site explains the principles involved -
http://www.distel.co.uk/DC_MOT_CON1.htm

I have attached a possible layout for consideration. The relay could be driven from the same power supply as the motor using a voltage regulator.

Some latching relays need a set and reset pulses on separate pairs of wires. Others use only 2 wires but the pulses have to be in different directions. The type needed here is a 2- wire uni-directional pulse model. Also called a sequencing relay. Whatever you call them they tend to be expensive!