Monday, November 29, 2010

Second glove... no field test yet.

Did the second glove.
Resistance is 18.0 ohms so it is pretty darn close to the other glove (without measuring the wire length before sewing it...)

Also did the Y-wire for connecting both gloves to controller.
Oh, and the controller is ready... sort of. Still needs to be soldered together but on breadboard it works just fine.
The only problem is: it is a single channel. And the reason for that is laziness...

Heat controller is microcontroller-based. PIC18F2580 has a builtin PWM-module, ADC input reads the value from 10k potentiometer and sets the PWM duty cycle based on potentiometer position, logic level MOSFET, connected to PWM output, controls voltage flow to gloves.
Could not be simpler than that.

In the test setup above, PWM duty cycle (Max) is about 300uS, period is 1.3mS. That gives gloves 6.7volts and that makes the wire to heat up to 48C-degrees.
Turning the potentiometer counterclockwise turns the heat down.

Next I need a plastic box to house the electronics.

Friday, November 26, 2010

First glove prototype ready and tested!

About one hour and 1.5meters of heater wire later:

Test rig:

Test result:

Excellent! The second lowest setting gives nice and toasty+38C temperature.
(The second highest setting gives +85C... Crispy?)

That means I can lower the pwm frequency and get the highest temperature down to +40C and that way there will be more precise temperature control. (Don't worry if you don't understand. Neither do I...)

Calculated heating power is about 10 watts. Tomorrow I will do the other glove and set them to be in series, that will lower the total power to 5 watts. Should be enough and that will also keep current draw in around 0.4 amps.

If all goes well, I will perform field test on saturday. Weather forecast says it will be a cold day. Just above freezing in the morning. Perfect weather for testing.

Saturday, November 20, 2010

UI getting ready...

It's time to close the lab for today.
Today I got the user interface sorted out.
Works more or less like this:

One number display, one knob to rotate, one button (will be embedded to knob later).

There will be four "channels" for four different heating circuits: Feet, hands, legs and torso. (Perhaps Socks, Gloves, Pants and Jacket)

Each channel has its own heat setting, in default mode device adjusts all channels equal amount up or down.

In default mode (right after powerup) display shows the global heat setting (ten levels 0-9).
With knob user can change this setting.

If user pushes button for more than a second, display starts blinking and shows the channel (S,G,P or J).
User selects desired channel with knob and pushes button for less than a second.
Display keeps blinking (indicates individual channel setting in progress).
Now user can set selected channel temperature, again ten levels 0-9.

After selecting desired heat level, user pushes button for less than a second and display starts blinking the channel id again (S,G,P or J).

Now user can either select another channel or push more than a second and device goes back to default.

Should be something like that but I have a feeling it needs some more thinking...

Wednesday, November 17, 2010

Getting cold...

'bout week ago we were riding around northern Arkansas with some pals. It was not exactly freezing but it sure was freaking cold in the morning(s).

Ok, it was below freezing but not much.

One of us had electrically heated clothes so he was the only one feeling warm and cozy no matter how cold the weather got.

Now when I checked the prices of such clothing, it made me think "How hard could it be"...
I definitely will not pay $1k for socks, gloves, vest and pants. No way!

Google found me some DIYers who have made heated clothes out of 30gauge hook up wire. I formed a plan to make heated insoles for my boots with such wire.

I told about this idea to fellow tinkerer Esko and he found one company, in internet of course (, who sells heater wire (or resistance wire).
I just ordered 50ft spool of "33 Gauge 3/38 Stranded Midohm/Alloy 180 w/8 Mils Tefzel"

In plain English that is 0.18mm diameter teflon (PTFE) insulated nickel+copper wire with nominal resistance of 3.572ohm per foot. Thin enough to me sewn into jacket liner etc. with a needle.

For controlling the heat I already have, from my flight simulator project, a pcb board with Microchip PIC 18F2580. That combined with logic level mosfets and some pwm-code will do a nice heat controller.

Stay tuned...