K8055 to control dimmable fluorescent ballast?

Kits PC Related Projects
1

I have a K8055 which I am trying to use to control the lighting in an aquarium.

Thanks to HOB’s easy program software :smiley: I have that side of things working and the plan in place but I have one challenge remaining that has me stumped.

I have 2 dimmable fluorescent ballasts that I would like to slowly bring up the brightness at switch on and slowly reduce it at switch off.

The ballasts are controlled via an onboard 10V signal and you simply connect a 100K pot across these signal lines to dim the ballast.

My initial hope was that I would be able to use the PWM output of the 8055 across the 10V signal line of the ballast but this does not fully work – I get about 5 levels of dimming but by the time the PWM output reached 5 (of 255) the light is fully off so it seems that the PWM signal is not suitable for this application – or perhaps it may be with a different frequency :confused: :confused:

So I guess I am trying to figure out a way to replicate a 100K potentiometer via an analogue/PWM output from the 8055 and some circuitry.

I suppose I could control a stepper motor and turn a pot this way but I am hoping that there is a non mechanical way to do this.

If anyone could help to point me in the direction it would be a huge help

2

well it looks like one option would be a voltage controlled resistor driven from the analogue outputs but from what I am reading they can be problematic and I am not sure that I understand the concept fully so would result in a lot of trial and likely even more error!

Another option would be a digital potentiometer but I would then have to convert the analogue output back to digital to send to the digipot

Or am I trying too hard? Would the right capacitor across the PWM outputs smooth the output and give me a more analogue signal?
I am afraid that although I can solder up a project I am woefully ignorant when it comes to the design side.