Apologies for such a long delay before responding. Life got very busy and I did not have much chance to continue with my new electronics hobby .
Firstly, thank you very much Ryan for your help.
You were correct that this set up does not (apparently) damage a usb port.
Unfortunately, you were also right to be concerned about my use of a car battery and the power draw of the motors! This choice was made as the project will be used on a motor home, and will be powered by the vehicle’s car battery.
The motors were salvaged from somebody else’s previous project. They appear to be some sort of heavily geared wiper motors (they turn very slowly, maybe 10 RPM when directly connected to the battery). Without load they draw a maximum of 0.6A @ 12.5V. I did not measure the stall current as I am concerned stopping the motors will chew the gearing. I’m also a reckless fool .
Before starting my tests I checked the voltage of the car battery. It was a ‘safe’ 12.5V.
I hooked up the Arduino to the motor controller as outlined in the MeanPC guide (arduinomega.blogspot.co.uk/2011/ … otors.html) to set STBY to HIGH and AIN1 to HIGH and AIN2 to LOW then applied various duty cycles to PWMA. All worked flawlessly, the motor spun at different speeds corresponding to the duty cycle. I hooked up a second motor and both motors behaved perfectly, even when simultaneously driven. After 20 seconds of operating the motor controller was cool to the touch. Very easy to set up and very pleased with the motor controller… until…
I then decided to try the motors in reverse. I spun the motors to full speed forward one at a time, braked them (AIN1/BIN1 = HIGH, AIN2/BIN2 = HIGH) one at a time until they stopped spinning then applied full reverse one at a time. The motors stopped but would not spin in reverse (they can do this fine when attached across a battery). The motor controller let out its usual high pitch whine but nothing else happened. I disconnected the battery.
I have now tried to get the motors to spin forward and everything appears to be completely dead. I have tried hard wiring AIN1 to 5V, AIN2 to 0V, STBY to 5V and then feeding PWMA with a 50% or 100% duty cycle and everything else I can think of. All connections seem good (checked with multi-meter) the motors are working when connected directly across the battery, the Arduino appears to be functioning correctly.
I suspect the spinning down of the motors and trying to reverse them may have stalled them and caused them to draw far more current than the TB6612FNG can handle. Any thoughts? Is there anything else I can test or is it time to invest in a slightly more hardcore motor controller, start taking LC spikes seriously and chalk one up to experience?