Low port#2 pin#16 voltage - PMDX-126 with jtechphotonics DAC PWM

[Bx3mE]

This question is posted on CNCZone too but with some changes to my setup since I posted there.

Im adding a Laser to my XZeroCNC Raptor.

 I have PMDX electronics (126, 107 and 134) for BOB, spindlecontrol and Geckodrives (203V) receiving data from a EthernetSmoothStepper (ESS) and controlled by Mach3.
 The DAC PWM is powered from the same 5V supply which is also used to power the ESS. PMDX is powered from 220V internal supply and Laser Driver board is powered from separate powersupply. Geckos are powered from an Automationtechnologies Toroidal supply at 56V.

 I am now adding a JTechPhotonics DAC PWM, http://jtechphotonics.com/wp-content/uploads/2013/05/DAC_PWM-Manual-V1.13.pdf,
 to my setup using the outputs from the second parallel port (port 2 pin 1,14,16 and 17).

 Symptom:
 When I in Mach3 click Mist toggle or Flood toggle the outputs in diagnostics view start to blink, the led associated with pin 16 and 17 light up respectively and the led on the DAC PWM lights up but the Laser driver power connector never goes up to expected 5V but stays at 0V.
 I would expect the relay to klick but it does not (maybe it is mor silent than I expect). The DAC PWM board does receive step and direction signals and also sends out pwm signal. When I skip using the DAC-PWM relay for laser driver the laser driver does read 255 different levels as expected but never reaches desired output.

 Investigating the source of the problem...
 I disconnect Everything related to the DAC PWM from the BOB (PMDX-126) and check output voltage, 0v at low and 4.3V at high. When I reconnect DAC PWM and measure again it shows 0V at low but only 2.7 at high.

For now im guessing that the 5V 10A supply im using drops voltage under load so the driver does not get enough supply but when I disconnect the laser driver excessive load should not be present but the PMDX still has low 5v output.

Im frustration to this problem im about to invest in a lab grade powersupply which should be able to hold up the voltage. Could I have connected something wrong or is my system under no load drawing so much power that a regular 5v 10A supply cannot hold up?

Any help is greatly appreciated!

[edited by Bob to add full URL for DAQ-PWM manual]

[Bob at PMDX]

Before I can try to figure out what is going on I need to know *exactly* how you have the PMDX-126 wired to the DAC-PWM board, including all of the connections to the DAC-PWM terminal strip with the Power, output relay enable, driver power enable, step and dir inputs.  I also need to know which output signal is controlled by your "flood" and "mist" buttons, so I know which input on the DAC-PWM  you are trying to control.  You can sketch a wiring diagram and scan/take a picture of it and post it here, rather than trying to describe what is connected to what.

For now im guessing that the 5V 10A supply im using drops voltage under load so the driver does not get enough supply...

If the output from the PMDX-126 is only going up to 2.7V when connected to the DAC-PWM, I don't think that is related to the DAC-PWM power supply drooping.  And that is easy enough to verify.  Put your volt meter on the DAC-PWM "Power In" and "GND" terminals and measure the voltage.  Does the supply actually droop?

Having the PMDX-126 output only go to 2.7V sounds more like something trying to overdive the PMDX-126 output (like a low impedance to ground or having the PMDX-126 output signal tied to an output signal from the DAC-PWM instead of an input.

[Bob at PMDX]

Whoa, I just realized something.  I don't know exactly what the circuitry on the DAC-PWM board is, but...  if the "OUT Enable" and "Driver Enable" inputs are directly connected to the relay coils on the DAC-PWM board THAT WILL NOT WORK WITH THE PMDX-126!!!  And could possibly destroy the outputs on the PMDX-126.

The DAC-PWM board's relays need around 75mA of current at 5VDC to energize.  The PMDX-126 is only capable of outputting 16mA.  Trying to directly drive the relay coil could indeed make the voltage on the PMDX-126 output pin drop to 2.7V.  And 2.7V may still be high enough to turn on the associated LED on the DAC-PWM board even though the relay is not energized.

Even if the PMDX-126 *could* energize the relay, unless there is a protection diode across the relay coil on the DAC-PWM board, the indictuve kick-back from de-energizing the coil could destroy the PMDX-126's output driver.

Alas, I cannot find ANY specifications on the jtechphotonics.com website for what input current is required on the two enable inputs.  Not on the product web page nor in the instruction manual.  That is a question you need to ask J Tech Photonics - "can the enable inputs be driven by CMOS/TTL outputs?" and "do the enable inputs directly drive the relay coils?".

If the enable inputs directly control the coils of their relays, you will need something between the PMDX-126 output and the DAC-PWM enable inputs.  You can use the PMDX-104 (http://www.pmdx.com/PMDX-104) or the PMDX-105 (http://www.pmdx.com/PMDX-105, see section 2.6 in the user's manual) for this purpose.

Bob

[Bx3mE]

I am the lucky owner of a still fully functioning BOB :)

I can indeed verify that the relay is driven directly from the input thus requireing more than 50mA on the output...

Which one of the pmdx 104 and 105 should i buy? what are the differences (other than comparing specs) what use can i have for the pricier option?

The DAC PWM Does respond to Step/dir signals, do i nedd additional electronics to be safe?

[Bob at PMDX]

I am the lucky owner of a still fully functioning BOB :)

I can indeed verify that the relay is driven directly from the input thus requireing more than 50mA on the output...

Which one of the pmdx 104 and 105 should i buy? what are the differences (other than comparing specs) what use can i have for the pricier option?

Luck sometimes works in our favor!  The PMDX-104 will be easier to connect, though it is a bit more expensive.  With the PMDX-104, you can wire two of the pairs relay contacts between the DAQ-PWM's +5V and the two "enable" inputs.  With the PMDX-105, you will need to add a diode from each of the DAQ-PWM's enable inputs to the +5V terminal to protect the electronics on the PMDX-105.

The DAC PWM Does respond to Step/dir signals, do i nedd additional electronics to be safe?

I would think that these inputs would be OK to connect directly to the PMDX-126's outputs as they are (well, *should* be) driving logic chip inputs on the DAQ-PWM board.  I can't be sure, but I think that is a pretty safe bet.

Bob

[Bx3mE]

PM SENT :D

[Bob at PMDX]

I just realized another possibility.  Are you using the 2 relays on the PMDX-126 board?  If not, you could use those relays instead of the PMDX-104 or PMDX-105 to switch the +5V to the two "enable" inputs on the DAC-PWM board.  They are way overkill for this, but if they aren't otherwise being used you may as well use them.

Bob