The Shop > Wood & Stuff
Drum/ Thickness Sander
S. Heslop:
I'm not even sure where the original circuit was. I just found it via a Google image search.
I was looking up more 555 stuff and took another look at that website I got the real simple diagram from and found a more specific one.
http://www.555-timer-circuits.com/motor-pwm.html
And built it! There's an error in the diagram with one of the diodes backwards, that I wouldn't have noticed except that the two diode thing looked similar to the one in your second diagram.
The results are pretty good. The wavelength stays the same for most of the range, plus the pulse width ranges from very narrow to almost fully on.
The slight sawtooth shape disappeared with a resistor connected in place of the motor like suggested.
I think I might stick with this one since it seems to be working fine. I'll have to leave soldering it up properly till tomorrow since I'll need the daylight for recording it.
Bluechip:
Have a look at the power rail while it's working.
The spikes may well be coming from there, you should really put a decoupling capacitor ( 22uF - ish ? ) right next to the chip Vcc pin to deck. The non-cmos 555's crowbar supplies like the devil.
IIRC the 7555 is the cmos version which does not do it so much ... :thumbup:
It'll work :ddb: in my working life I've scoped industrial stuff and it's grim :zap: but it ekkles ... :lol:
Dave
S. Heslop:
Got the circuit made, with the decoupling cap and all which really helped reduce the spikes. Hopefully it'll work just fine with the bigger motor, that i've yet to buy.
It's ugly but i'm still really pleased with it. I should probably try get the flux off. I wonder if methylated spirits will work.
Thanks Dave for the help while building it!
vtsteam:
I've been following along with great interest, Simon, just not a lot to say, except keep up the good work! :coffee: :thumbup: :beer:
awemawson:
I use spray carburetor cleaner and an old toothbrush to remove flux residues after soldering. If you are neat changing a component it's hard to tell you've been there :clap:
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