Operating a DMX controller with a footpedal - help and guidance please !

[rogerds]

Newbie to the forum -please be gentle and forgive any unintentional etiquette breaches!
No electronic knowledge or theory but keen to learn.....
I'm a guitarist in a band and we have a small lighting rig run by a DMX controller but i've been trying to find a way to operate it using footswitches to select the various pre-programmed lighting 'scenes'.
so - bought cheap used controller looked inside and saw the scene selector buttons seemed to be mini momentary contact switches. - I thought 'if i soldered leads to the contacts and fed them to momentary footswitches i could mimic pressing the buttons to select the scenes and also change the 'banks' up and down' (8 scenes to a 'bank')
That way i could select lots of different lighting programs using the footswitches
The theory was to feed the leads in the controller to a DB25 pin socket - ad do the same thing using an old food warmer to construct the foot pedal with 10 switches - then connect them using a DB25 cable and hey presto!

Hmmm..Worked with some scenes (3,4,6,7,8) but 1&2 activated scenes 7&8 and 5 activated the 'blackout
and..... this also happened when pressing the buttons on the controller with the DB25 cable plugged into the controller but NOT into the footswitch (but works fine manually when no cable connected) - have checked connections several times
Pics below may show what i've done (soldering has been done and re-done several times so is not as tidy as it was at first !)
Thanks for reading and any ideas what is going on (words of one syllable please

 

[Alec_t]

I suspect the added inductance and capacitance due to the long leads is the cause of the problem. Do you have access to an oscilloscope to see what scanning voltages are being applied to the buttons by the controller?

 

[rogerds]

I suspect the added inductance and capacitance due to the long leads is the cause of the problem. Do you have access to an oscilloscope to see what scanning voltages are being applied to the buttons by the controller?

thanks for coming back - i've learnt something already ! - you mean that a voltage is continously (or rapidly) applied to the buttons and 'altered' when the button is pressed.... but no... no oscilloscope
If what you are suggesting is right - is there a way round it? - roger

 

[Harald Kapp]

If what you are suggesting is right - is there a way round it?

Check it first: use the same switches but very short wires to see whether that works. If so, Alec's thoughts are correct.
What I can envision is placing the contact elements next to the controller's pcb (where you currently solder your wires to) and control the contact elements from remote (via the footswitches in your box). There are several ways to do this. One rather simple way is using small relays with a single contact (normally open, SPST). Find ones with a coil rating of 5 V ... 9 V. Put a 9 V battery into the box with the footswitches, use the footswitches to activate the relays in the DMX controller box. That way:

• You avoid long wires for the signals of the DMX controller, just short stubs from teh relays to the pcb.
• You have full isolation of the contacts and the footswitches. If someone somehow were to accidentally put power of any kind into the DB25 connector, worst case is the relays will be damaged, not the (I assume) much more expensive controller.

Disadvantage: you need another 9 V battery. Maybe you can tap into another power supply that's already present? It doesn't have to be 9 V (this is simply a handy format on stage, I guess). Use whatever voltage is available as long as the relays' coil voltage matches this supply voltage.

 

[rogerds]

i like that - and i understand ! - and same switches with short wires do work - sincere thanks to both of you - i'll try that and post how i get on
I have a 9v power supply at my feet powering guitar effects pedals so easy to take a tap off that
roger

 

[rogerds]

sorry but one more question-- what sort of amperage is required to activate a 'normal' small 9v coil relay ? I ask because my power brick i use to power my guitar effect pedals has a maximum output of 2A or so and I could be running 4 or 5 pedals at 300 / 500mA each and wouldn't wish to affect the effects and hence the sound.... I did try googling but couldn't seem to find an answer... thanks again

 

[Alec_t]

Plenty of low coil current relays available, such as this. (<20mA).

 

[rogerds]

just to say thanks to you all
now have gigged with working pedal / controller system! and works just as it should
used a 9v battery in the footpedal to activate the relays - as suggested - which fitted quite neatly inside the controller unit itself
so i can now select all my pre-programmed lighting scenes whilst i'm playing- brilliant !
it may not have been electronically taxing to you but it makes such a real difference to me
thanks again
roger

 

[Alec_t]

Good to know it's all working.