CNC plotter 1800 x 80cm, first build, questions and queries.

[Doddy]

The semi-random effect is as I'd expect. Even using a N/O push button rather than just a bit of wire you're going to get something called "contact bounce" where pressing the button generates a whole bunch of On/Off transitions as the button contacts literally bounce against each other. This usually dissipates within a few milliseconds, but you can certainly get more than one "contact" per press and with a fast stepper setup (usually rated into the hundreds of kilohertz - sub 10 microsecond territory) you might expect a fairly random number of pulses / rotational steps. But, they should be in one direction only.

I'm going to largely ignore your voltage measurements - because I don't understand quite what you've written. I *think* you're saying with E-Stop off you confirm you have 5V (all measurements taken with the meter's black lead connected to 0v) supply to the BOB, and 5V on the EN enable pin, and the LED 'output status' is illuminated, and with the E-Stop on you confirm the EN enable pin falls to 0V and the 'output status' is not illuminated? That's what I'd expect to happen and is again a good thing. It indicates that you have power to the board and your e-stop circuit is operable.

My concern now lies with no sign of life from the LED indicators on the outputs from the BoB. With the-estop OFF : Using the cursor keys to pseudo-move the X-axis in one direction or another you will be changing the X-DIR signal between 0v and 5V (can't tell you which way around) - which should illuminate/extinguish the LED on output pin (3) on the BoB. I'd use that as your primary sign-of-life from now on.

So, your stepper drivers are showing signs of life, together with your motors, so I think it's time to concentrate on the board and the Mach 3 interface to this.

1) My first question is - has you witnessed the actual computer that you're using with Mach3 successfully drive this board?, I think from your description - no? The problem here is chasing a potential ghost - if the PC is not set-up correctly then you can probe the board all you like and there'll still be no life.

2) Are you using a full 25w wired parallel cable between the computer and the BoB?, have you tried a quick continuity check to make sure pin-1 goes to pin-1 etc through pin-25? (if you found a random 25w cable it *could* be a serial cable with only a small number of wires connected, and some of those possibly swapped). Check the basics.

3) Of interest - on the BoB - there's a 3-pin jumper header labelled "JP1" - there should be a shorting pin connecting two of the pins together - which two?

4) Would you be confident to ***CAREFULLY*** measure the voltage on pin-1 of the 25-W D-type that the computer plugs into, with the system powered. I'm talking about connecting the meter black lead to 0V and carefully probing the PCB where the pin-3 is, and measuring the voltage with the X-Axis moved in one direction, then again with the X-Axis moved in the opposite direction. In one direction you're expecting a voltage less than perhaps 0.8V and in the other direction greater than perhaps 2.5V.

5) Much easier - could you do this again on the PC. insert a couple of pins or bits of stripped solid strand wire (paperclip?) into pin 3 and pin 25 of the PC parallel port and measure for each direction of X-axis travel. If you can provide a photo of this for our amusement (and validation) - this is getting to the point where we should be able to understand the PC->BoB communication - I think the BoB's basically functional, so this is important to understand why the BoB is not seeing the commands from the PC.