Useful tidbits, interesting projects or ramblings of a mad man: you decide

Debug RS232 Connection to StepperOnline CL86T Driver

Between all the cheap stepper motor drivers I've worked with over the years, the StepperOnline products seem to be the best for quality and reliability. Their documentation leaves a little to be desired though.

I've run into a problem with a CL86T closed loop stepper driver where I need it to apply more force that it's capable of. This should yield in the motor determining it's not capable and switching to an alarm condition. In this use case it is not doing that.

After some thinking, I came to the conclusion that the issue was probably the number of steps of allowable error. To be sure, I needed to get into the settings for the driver. This requires their software, an RJ12 (or RJ11) to USB serial cable.

The Problem

I ordered an RJ11 to USB adapter from Amazon thinking it was a slam dunk to make connect the software and controller. After receiving the adapter, downloading and installing the software on the computer and connecting the driver and computer, the software reported communication error.

Some research found that a potential issue was the TX and RX connections were reversed. The test to determine if this is the problem is to use a multimeter between the signal ground and the TX pin and the same for the RX pin. If one pin shows a voltage and the other does not, then the pins are reversed.

The Solution

I figured I had a couple of options. First, cut the new RJ11 cable in the middle and do a hack job switching the TX and RX wires. Second, cut the RJ11 end off and replace it with a new one with the TX and RX leads swapped. Third, cut the new cable and just use the RJ11 end and a short section of wire into a DB9 connector then use a DB9 to USB serial adapter.

I opted for option three because I had the DB9 connector and the hack job in the middle of the cable felt wrong.

RJ11 to USB Serial Adapter

With a properly working cable, the software was able to connect without a problem. Immediately I saw the setting issue. The maximum allowable position error was set to 1,000 steps. With the micro-stepping set to 2,000 steps per revolution, this means that it would have to turn a half turn before an error would be thrown.

In most application where a gearbox or lead screw is used, this half turn would probably be perfectly fine. But in my application, the motor is a direct drive to feed wheel so the half turn is a huge amount. I've reduced the setting down to 100 and will test again.

Ultimately, the direct drive connection will have to change since it is running out of torque to move.