6 Channel Dew Heater Controller

[RogerTheDodger]

Malc, have you seen this pwm design? simple and cheap.

http://www.iceinspace.com.au/forum/showthread.php?t=63666

[malc-c]

The PIC approach also has it's complications, in that it would need cleaver use of interrupts so that you get six PPM channels all pulsing at individual rates, otherwise if using simple delays the 1st channel would have to wait for the last channel to end before looping back..... Maybe the no-can-dew heater with 556's would be better.

Googling around a I found some schematics that use TIP120 darlingtons, and others that use MOSFETs... any advantages / disadvantages using darlingtons ?? - I have 5 x TIP126's in my electronics box...

[malc-c]

Malc, have you seen this pwm design? simple and cheap.

4 channel PWM Dew heater - IceInSpace

Nice find, and thanks for the contribution. My only concern was the bullet point

Cheap design. Can be made for around $100 or less depending upon your access to odds & ends.

At that price it would be almost as practical to purchase the HiTech Asto unit.

[RogerTheDodger]

Hmm, just looked at the part prices and I don't see how it'd be that much...

[Gina]

LM555/556 the way to go KISS

[Reggie]

Arduino code would be much simpler than the pic stuff, 6 analog inputs, 6 pwm pins, all running at different duty cycles, can scale the analog input range to match the pwm output range. (1023 to 255), would be very simple, don't need to use blocking delays, would probably need 2-4 caps, maybe some resistors between the outputs and fets.

Certainly nowhere near $100 of kit The fets on the ice in space board are super cheap, I'm not entirely sure where those prices are coming from. aaaaahhhh, wait a minute, that's an australian forum, that'd be why it's expensive, those are australian dollars and those poor guys get charged the earth for components!!

so, I reckon about £4-5 for an atmega168/328 chip, £5-10 for your fets, couple of quid for your resistors and caps, another quid or 2 for some transistors and it's up to you what you spend on connectors, fuses etc.

[malc-c]

Well I ordered an Astrozap dew heater from FLO for the ST80. The measured resistance was 28 ohms and I'm pleased to say that the unit drives that without problems. Using Ohms law that equates to around 493mA at 13.8v.

I've been thinking about the PWM versions, and may end up using the 556's or programming a PIC later. For now I'm going to run with what I have, but with one further modification... change those ruddy supa-bright blue LEDS for nice dim red ones !

[Gina]

How I hate bright blue LEDs!!

[malc-c]

How I hate bright blue LEDs!!

Well they're gone now

Replaced the 6 super bright blue leds with standard red ones and it looks good. Also added one additional socket connected to an 8v regulator to supply the 400D dSLR, so hopefully no more having to replace batteries half way through a run !

So what started out as a basic 6 ch dew controller has now ended up being a compact power box and controller in one