Help with wiring piface to an L298 h bridge

I have a Pi-Face which I have successfully used to switch on and off some LED's but I'm a bit stuck on taking the next step - to drive a robot chassis.

I purchased one of these l298 motor drivers but I'm completely stuck on how to connect up the pi faces open collector outputs to the l298.

From searching about on the net it appears that it definitely possible but I just cant figure it out.

johnbeetem over 13 years ago

Open collector outputs can only pull down to ground, so I suspect you need a pull-up resistor (say, 4.7K Ohm) to 3.3V or to 5V for each signal that connects to an L298 logic input. According to my ST L298 data sheet, it expects TTL-level inputs and anything over 2.3 V is considered logic high.
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e14 Contributor over 13 years ago in reply to johnbeetem

I did try putting together a pull up resitor but I was obviously wireing it wrong. I became a little confused as to where the open collector was wired in. Do you have an example diagram or something that shows how to make the circuit?
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Problemchild over 13 years ago in reply to johnbeetem

Indeed the inputs are already TTL compatable and as John says you'll only need a pull up of a few K to pull it up to the right logic level.
The microchip I/O expander is a 5V part so I assume you can pick 5V up so you can certainly drive that L298.
At that point I'd theve an Arduino shield example circuit to give you an example of how to drive the motor.
Remember you will need a seperate rail for the motor supply generally arount 2-3V than the required operating voltage of the motor to allow
for volt losses inside the chip
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Problemchild over 13 years ago in reply to e14 Contributor

The resistor goes between the output of the ULN22803 and 5V .
I would also take a min to actually measure the voltage at the out put before you start to see if your program is actually changeing the voltageon the pin you expect!
Easy done
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johnbeetem over 13 years ago in reply to e14 Contributor

Richard Andrews wrote:

I did try putting together a pull up resitor but I was obviously wireing it wrong. I became a little confused as to where the open collector was wired in. Do you have an example diagram or something that shows how to make the circuit?
Wikipedia to the rescue!

http://en.wikipedia.org/wiki/Open_collector
http://en.wikipedia.org/wiki/Pull-up_resistor

Some people "google" things, I start with Wikipedia. I get a higher signal/noise ratio And I do make an annual donation
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Problemchild over 13 years ago

Taking a look at the Ebay link I see it has seperate power and enable links etc.
to test I would connect the motor to the output then power the motor supply.
The built in Regulator will supply the 5V for the logic.
If the motor supply is less than 7V then you will need to supply the 5V externally as the regulator needs at least 2 V to opperate well

Don't bother to connect to the pi try setting the inputs to the correct logic level by connecting them to GND or 5V and see if you get your
desired result if not then your program logic is at fault and you best take another look at the L"(* datasheet and the truth table in it .
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Problemchild over 13 years ago in reply to johnbeetem

Surely E14 has the best noise figure out there
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