The PWM cct only uses 1ma
1 x 100 nf Capaitor
1 x 1 uf Capaitor
1 x 555 timer chip
1 x 8 pin socket (optional)
2 x diodes (not zenner)
1 x 100k Potentiometer
22 awg wire
Transister (suitable for your project)
5mm drill bit
Step 1: Prepare Strip Board
The tracks under the ic will need cutting to do this a 5mm drill bit is used this will remove the copper track where it is needed.
For this project we will use a small piece of strip board 12 strips wide and 1 1/2 inch long.
Remember when cutting the tracks the underside is in reverse
Step 2: Add Components
When soldering components it is good practice to solder the lowest profile components first, and where possible keep components flush to the board
we shall start with 22 awg wire links
next to solder are the diodes note there direction
followed by IC or socket and capacitors. (if using a IC socket remember to insert the IC at the end)
Finaly the Transister, Pot wires and supply wires. (Check pin out of transister that you are using)
Step 3: Testing
connect the suply wires to power source 5v to 15v should do observe the correct polarity +ve to +ve etc. during testing check that components dont get hot.
The only component that may get hot is the transister under full load if neccersary fit suitable heat sink.
By swapping the min max pot ends changes the direction of rotation for off to full on.
probe the gate pin or base pin on the transister and rotate the pot from one extreme to the other and finaly centre, Check that the pwm signal is square wave and that the duty cycle changes apropriatly.
Frequency Meter & LED
probe the gate pin or base pin on the transister and rotate the pot from one extreme to the other and finaly centre the frequancy (aprox 10 Hz) should change but not significantly this is a function of the RC on the 555. True PWM the frequency is constant.
Take a suitable Load (LED and resister in series) and connect across the output turn the pot from extreme to extreme again LED should brighten and Dim accordingly.
To test under power a siutably rated load should be used as Im looking at using an approx 3ohm load (ie the heater cable) wire up and start test on low PWM checking the tempreture of the transister. Idealy the transister shouldnt go above ambient tempreture any power loss ie heat in the transister isnt power in the heater.
Step 4: Clothes Heater Wire
I have now finished this project unfortunatly the IRF1730 TO-220 over heated and the wire didnt, However I found an smd AO4406 on a trashed laptop motherboard it works fine