Jem DMX module for TechnoFog

[Neil Hampson]

So I've had an old TechnoFog machine for about 20 years, it's an analogue controlled machine and I have a Multi-function controller with a manual and timer and a Jem DMX controller. The Controller suffered a stage accident and I have had to re-wire the internal connection to the PCB board and the test/purge button. Since the repair the 0% output is slightly too high meaning the smoke machine is always wisping smoke out. I have compared the outputs from the other controller and I get the following:

 

Multi-Controller: 0% 1.62V, 100% 10.7V with a supply voltage of 16.9V

DMX controller: 0% 1.95V, 100% at 11V with a supply voltage of about 15V

 

When I re-connected the wiring there was a diode in the box loose that looked to have been connected to the Purge button but I do not know exactly how this should have been wired up. Is there someone with one of these units that might be able to tell me how the three pins are wired. Other than the DMX input there are only three wires into the unit, 18V power, 0V and a signal return. My initial thoughts is either that the diode is important in the circuit somewhere, or ther is a fault on the unit, other than the overvoltage at 0% it appears to work OK. My other thought is to put a potential divider across the signal output to drop the output voltage by 10% Can anyone advise what the return voltage should be to not fog, but still force the unit to heat? Or is there a trim pot inside the Fogger it reduce the output thershold.

 

Sorry in advance for the long post...

[timsabre]

The voltage is nominally 1v to heat and not fog. Below 1v it turns the heater off. I'm not sure what exact voltage it actually starts fogging at.

 

Perhaps the diode was in series with the control voltage? This would drop the voltage by about 0.6v

[Neil Hampson]

Of course. The volt drop across the diode would be fixed and not proportional to the voltage. When I saw the diode I immeasurably assumes it was to sip the switch input from back feeding the DMX electronics, it never occurred to me that it was a dropper. I’ll give this a go thank you.

[Neil Hampson]

Of course. The volt drop across the diode would be fixed and not proportional to the voltage. When I saw the diode I immeasurably assumes it was to sip the switch input from back feeding the DMX electronics, it never occurred to me that it was a dropper. I’ll give this a go thank you.

[timsabre]

Well it would actually be there to stop back feeding. The output voltage from the DMX interface has been designed to have the extra voltage so that it's correct after passing through the diode.