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I dont intend to go into the ins and outs of this circuit, just how to make it. you can save pennies by using reclaimed components from old circiut boards but these parts are all cheap and readiy available.  The Circuit here is 144Hz and R2 (10k) is not needed for my needs, The circuit below is for a fan and R2 switches the fan on in a PWM failure ie fail safe.

The PWM cct only uses 1ma

Parts

Strip Board
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)
Project box.

Tools

wire cutters
solder
soldering iron
5mm drill bit
saw

Step 1: Prepare Strip Board

Strip board consists of copper strips with holes predrilled at 1/10 inch pitch. The components sit on the plain side the legs then solder to the tracks.

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

First Prepare the Potentiometer, cut 3 equal lengths of wire aprox 2 inch long strip of 4mm of insulation from all ends and sold one piece to each of the 3 pot terminals.

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.

Scope

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.

Power Testing

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

As I am interested on using these on my Motor Bike I have placed the heater where I feel the cold the most.  The photos were taken before i fitted inline 5.5mm power Jacks.


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

<p>It appears that in the circuit diagram pins 7 and 3 of the 555 are reversed.</p><p>Pin 3 is the output, pin 7 goes to the pot. </p><p>The board is correct.</p>
In the board layout 8 is not connected to anything though its clear in the schematic.
Hi. Thanks for the tutorial. I'm not sufficiently competent to spot problems myself - are the instructions above corrected (if correction was necessary)? I don't know much about transistors but I don't want to use on that ultimately overheats. What do I need to know to select one which will be suitable? <br> <br>The ready-made PWMs on eBay are quite expensive, even though they're coming from China. Is that because they're more energy-efficient? <br> <br>Thanks for any insight :)
I dont think the Chinese PWM ccts are more efficient The One above only draws 100ma and I dare say that a choise of more efficient 555 couls improve the effieciency further Using a Mosfet Transister ensures operation at most effieciency as the gate has an extreamly high impedence. <br> <br>As regard the choice of transister things too consider <br>1, Physical size of transister <br>2, The Maximum Current in the Load I would ensure that the transister can carry 50% more max current than the load will draw (non Pulsed) ie 100% on time. I have found many in a 220 pakage capable of carrying in excess of 60amps and 120 amps pulsed. <br>3, The Price <br>4, Heatsink The smaller the drain source on Resistance the Lower the heat losses will be. <br> <br>But Finaly the use of a heat sink can be determined by testing your PWM under full load and measure the case tempreture of the transister. as a rule of thumb if you can hold the case without burning your fingers on full load you can probably get away without a heatsink. <br> <br>I would recomend you select a range of Mosfets and buy a pack of 10 or 20 or each type and keep in yr kit. and select the best for your project <br>rated at <br>150ma ta92 <br>2a ta220 <br>16a ta220 <br> <br>I hope this is of some help The CCT schematic is correct C3 &amp; R2 are optional C3 acts as a supply smoothing cap and R4 is a safety feature which switches on the transister if the 555 cct fails if R4 is conecter from the gate to Ground it will switch off the transister if the 555 cct fails
Been looking at your project and to me it looks like you have forgot the resistor. It looks like pin 7 of the 555 is directly connected to pin 4 and D of the transistor. Pin 8 seems to be connected to nothing.
Also I see 3 caps on the layout, but only 2 on your board?
And your part list is not consistent with the layout.
The Cap C3 is missing from The board and parts list well spotted. It isnt crucial to the operation of the circuit it is there to remove ripples in supply. <br>Pin 7 is connected Directly to the transister Gate, Pin 7 being an Inverted Pin 3 (outout). Pin 8 is directly connected to pin 4 and there is a resistor between pin 7 and pins 4and 8. It is clear in the drawing I can see.

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