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0-10V Eltec dimmer modification to ArtNet... zero point crossing


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Apologies if this isn't the right area and should be in Workshop or similar.

I've got two old Eltec 3-channel Alphapack style dimmers that run on 0-10V. Partly to see if I can, and partly because they would be of use, I'm trying to bypass DMX entirely and see if I can modify them with an ESP32 to run directly on ArtNet. (I've got the ArtNet reception working on an ESP32 before so that isn't really the issue.)

Rather than trying to replicate 0-10V out of a ESP32, I was going to try tap into the circuitry to trigger the triac directly. It has 3x BTA16 triacs for the 3 channels.The dimmer has a ULN2004 transistor array that seems to do the Triac triggers an attaching an IO pin to this seems to open the triac. As I don't have the timing for dimming I just hit it every 1ms and it seems to open fully. The spec sheet says it needs 6V to trigger but it seems to work at 3.3V.

In order to do the timing for dimming I'd need to find a zero crossing trigger to do the timing from. Would there seem to be one on this board? Is it the transistor down on the bottom right by the earthing to the case and the finger? That seems to be connected between earth and an AC voltage which I guess would cause it to square wave maybe?
I haven't got a scope to have a look at it.

(I know there's all sorts of other problems like whether I can do the timings for the triac whilst also receiving ArtNet on the esp, how it'll get wifi within an earthed box etc, but it's more of a playing around to be honest to see if I can)




Edited by TomHoward
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Hmmm. In this situation I've always tried to minimise the modifications to the host equipment so that it is easy to restore the original operation if things go wrong. In this case there's the complication of high power live circuitry and isolated low voltage parts that are accessible to the outside world, all in the same enclosure. I'd be inclined to modify the signal circuits in the dimmer pack to take a 0 - 3.3V analogue signal from the ESP32 (It's a 3.3V device). Use the analoge outputs from the ESP32 to control the dimmer pack in the conventional way. The ESP can be put under a plastic box 'lump' on the external metal dimmer case to let the RF in, or a suitable miniature 'rubber duck' antenna added to the case to feed the ESP inside.

Just my suggestion......


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If this was me I would do it using a op amp comparator with a esp32. This way you still have the protection for the ESP and also got your 0 crossing timings.

I have modded a few old dimmers in the pass but I would try and keep much of the original circuit as would save a lot of problems as flickering of light when dimmed low, also video cameras will see a light flicker even if we can't.

I forgot to add above if the ESP gets any voltage above 3.4v-3.5v max can kill it dead. I have been here and killed a few. so doing it via a op amp comparator will be the best. There is not many components need to do it this way.

Edited by dmxlights
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Thanks, I'll see about driving the op amp from the ESP32. I'm not planning to connect into the high voltage side of the circuit, do it all from signal side. The ESP32 is WIFI in so hopefully not too much risk to a wider data circuit, although being in the box is a problem but I'll get it working with a cheap one first before I buy one with an external antenna.

I think the way the original circuit is working is with a saw tooth wave maybe ramping up or down, and an op amp comparator. My thought is that transistor at the bottom right may switch with the AC frequency so I might just try borrow a scope and have a look. This would make sense as I couldn't work out how the original circuitry changed from a voltage to a timing.

I appreciate the thought about not modifying too much but the alternative is throwing it in the bin, there is zero chance I will ever want to run it on 0-10V again. I'm more playing with it and if it ends up useful so be it.

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I made a zero cross detector for a microcontroller based project using a bidirectional opto isolator (the type with back-back diodes) fed directly from the mains through a resistor. Gave me a nice narrow 'off' pulse at the zero cross. I've just spent a fruitless half hour looking for the damn thing in my hideously untidy workshop so I could tell you exactly what I did but I think I just drove the opto directly off the mains through a 470k resistor. That's an eighth of a watt so a half watt resistor is plenty big enough. I see I have some SFH620A-3 in stock so that'll be what I used. RS 699-8253


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Thanks I did think about that too as there's some spare pads down on the bottom left behind the pin headers and I assume I could run it from the low voltage side of the transformer too. I might just add my own zero crossing as I know it'll be reliable but be interesting to know if it is already on there 

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They're not suitable for phase control dimming. Those are what you use when you want to trigger a triac only at the zero cross (eg. for driving a heating load). With phase control dimming you're looking for the zero cross so that you can time from then when to trigger.

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Firing the triacs is working fine direct from the ESP GPIO pin into the Darlington pair IC.... I have the firing working it's just the timing for the zero crossing I need. I tried something out of that transistor but it wasn't a clean trigger so I might try add my own zero crossing circuit and try that 

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