Homemade heated vest controller?

I just got a hand-me-down heated vest. It has no controller. I looked at the site and they are available, but I don't want to spring for the $70.- for it. I could bodge up a really Neanderthal resistance based controller, but they end up dissipating power in the added resistors. So I was thinking that I could do something micro-controller based that would control the heat by varying the duty cycle. I should be able to use some power transistors as a switch and they would not dissipate much power, or I could go with a relay based solution. I was also thinking that I could incorporate a thermal sensor and create a feedback loop. Issues: my EE skills are poor at best, software is what I do. Anyone have any pointers or suggestions?

Research pwm controllers.

[yorkie_chris]

I'd use an atmega328
Link the ADC to a variable resistor or some sort of lo-hi-off 3 way switch, then one or two mosfets to control it through pwm

You might also want to look at arduino, it's a slightly higher level programming language. I've been using C for some diving stuff and to be honest it's giving me indigestion. By the time you've finishd you might wish you'd spent the $70... will be fun though!

[Mark_h]

Or just have a switch. If cold torn to -On. If warm enough turn to - Off. Replace with a thermostat inside the jacket if you find you are turning it on/off too often. Or are the elements so powerful you'd end up basted?

[keith_d]

Originally Posted by yorkie_chris

I'd use an atmega328
Link the ADC to a variable resistor or some sort of lo-hi-off 3 way switch, then one or two mosfets to control it through pwm

You might also want to look at arduino, it's a slightly higher level programming language. I've been using C for some diving stuff and to be honest it's giving me indigestion. By the time you've finishd you might wish you'd spent the $70... will be fun though!

Sounds like vast overkill for a heated vest. Just use a variable duty cycle oscillator (ICM7555?) and a high current FET switch. If you're not warm enough turn up the duty cycle.

[yorkie_chris]

Originally Posted by keith_d

Sounds like vast overkill for a heated vest. Just use a variable duty cycle oscillator (ICM7555?) and a high current FET switch. If you're not warm enough turn up the duty cycle.

That would probably be a better and cheaper alternative

I should add the caveat to my earlier post "I know nothing!"

Originally Posted by yorkie_chris

I'd use an atmega328
Link the ADC to a variable resistor or some sort of lo-hi-off 3 way switch, then one or two mosfets to control it through pwm

You might also want to look at arduino, it's a slightly higher level programming language. I've been using C for some diving stuff and to be honest it's giving me indigestion. By the time you've finishd you might wish you'd spent the $70... will be fun though!

I've been looking into arduino, especially since I'm contemplating a brake and turn signal controller also. I enjoy C, haven't done it in a while. Don't much object to paying the money per se, just to paying it for a pot and a couple of wires.

Originally Posted by Mark_h

Or just have a switch. If cold torn to -On. If warm enough turn to - Off. Replace with a thermostat inside the jacket if you find you are turning it on/off too often. Or are the elements so powerful you'd end up basted?

The resistance on the elements is 3ohm so max dissipation wil be about 50W, so should not cook. Besides I like to take projects like these as opportunities for learning, e.g. about power MOSFETS, software controlled feedback loops, sensor interfaces, etc.

[embee]

Plenty of stand alone off the shelf 12V pwm controllers available for pennies, like this for example . They are often described as motor speed controllers. At that sort of money I wouldn't bother messing about making anything, just put it in a box.