My First Pulse Width Modulator Mod

[iuseaspork]

OOPS... Dupe

 

[jrm850]

The freq is roughly 2.7Khz. If you right click the scope in that applet you can check the view freq option.

Can anyone tell me the frequency this is running at? I'm playing with cap values, but I just can't figure out what the freq is.

Also tried eliminating R1 and R2... Is this OK for almost full control over the duty cycle? Are there other things that they are doing in the circuit? I want almost full control to test both very high and ultra low resistance atties on this with high C rate lipos.


Circuit Simulator Applet

Without both R1 and R2:

Circuit Simulator Applet

If the one without the extra resistors is ok... here is my parts list:



1 1 IRLR6225TRPBFCT-ND MOSFET N-CH 20V 100A DPAK 0 1.47000 $1.47
2 1 SBH-331AS-ND HOLDER BATT W/COVR 3AA ON/OFF SW 0 1.94000 $1.94
3 2 497-1963-5-ND IC OSC MONO TIMING 500KHZ 8DIP 0 0.42000 $0.84
4 10 CF18JT47K0CT-ND RES 47K OHM 1/8W 5% CF AXIAL 0 0.06500 $0.65
5 1 987-1067-ND TRIMMER 5K OHM 0.25W TH 0 2.02000 $2.02
6 5 490-5401-ND CAP CER 0.1UF 50V RADIAL 0 0.14000 $0.70
7 2 1N5819-TPCT-ND DIODE SCHOTTKY 1A 40V DO41 0 0.42000 $0.84
8 1 EG4722-ND SWITCH PUSH SPST-NO 2A 48V 0 4.59000 $4.59
Subtotal $13.05

 

[iuseaspork]

Thanks. You also have to have 2 cycles show up in the scope before it will show. Finally have it!

 

[iuseaspork]

OK... Screw being broke! The stuff is on the way!

 

[iuseaspork]

OK... After actually connecting the 555 to ground (duh), It works! It works marvelously. Unfortunately, my meter will only read that it's 8volts no matter what the duty cycle. I'm also unable to check the frequency since I don't have a O-scope. Hope the epoxy cures on my test mod enough for me to take it to work today!

 

[jrm850]

There are free sound card based oscilloscopes you can download. Winscope and Zelscope are two that come to mind.

 

[bstedh]

Just use your Perception meter. It is way more accurate... =]

OK... After actually connecting the 555 to ground (duh), It works! It works marvelously. Unfortunately, my meter will only read that it's 8volts no matter what the duty cycle. I'm also unable to check the frequency since I don't have a O-scope. Hope the epoxy cures on my test mod enough for me to take it to work today!

 

[iuseaspork]

Here it is with a filter cap that made it even better!



Edit... Filter cap disconnected. (The cap) Was heating up too much. I suspect using a low ESR cap would probably be okay. I used a 22 uF cap for my application to adjust from a square wave to a saw tooth. Still working great with my rebuild-able genesis CE2 using a square wave, but probably harder on the batteries (though, maybe not considering all of the waste heat from the capacitor???!).

...Oh, and I know I should be using matched batteries. I simply do not have any.

 

[iuseaspork]

Oh yeah.... Had to mention that my design is in the 2.5-3.5khz range taking into account tolerance. This is in the audible spectrum and DOES in fact emit a tone when certain cartos are used. There is obviously some movement going on in the carto. Wheather that is a good thing (aiding wicking), or a bad thing (reducing life span) I'm not even going to speculate on. If I make another I will aim for 20khz. Shouldn't be able to hear that unless someone would really have exceptional hearing.

 

[MastiffMike]

Ummmm, I can hear it from here!