My First Pulse Width Modulator Mod

[bstedh]

Two things...

Using your finger to hold the wire on the battery is not a good idea. That contact point get real hot real fast... Owwwch

Never let idiots like me around electronics. The alligator clip I was using to clamp the negative MM lead to the fet was shorting against the cap giving me the same issue again. Nothing like causing you own circuit issues and blaming the device for your stupidity....

 

[Java_Az]

Two things...

Using your finger to hold the wire on the battery is not a good idea. That contact point get real hot real fast... Owwwch

Never let idiots like me around electronics. The alligator clip I was using to clamp the negative MM lead to the fet was shorting against the cap giving me the same issue again. Nothing like causing you own circuit issues and blaming the device for your stupidity....

I have found that if you have a nice ice cold beer handy it will cool your fingers down really quick in situations like yours. This is why i consider Ice cold beer a necessary mod tool.

I been trying to get the the 555 to work off a P channel mosfet with no luck so far. Supossidly if you take pin 4 low insted of high the output should sink current. Wish i had a decent N channel to run it off of. I just have a cheap radio shack one.
Did you get those boards in the mail yet. Was surprised to find my Blue solder mask got here today. China to here in like a week i was surprised.

 

[bstedh]

I have a crapload of nFets, I will drop some in the mail to you.

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[bstedh]

I got the boards and they look really good. I just hope my solder ability is up to the task.

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[Java_Az]

I got the boards and they look really good. I just hope my solder ability is up to the task.

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Yeah 0603's are small. I wouldnt even try it without a magnifine glass or what i use is a visor like these

But i am old as hell and dont see quite as good as i did in my younger days. Even so I think you would go blind pretty quick trying to solder those with out one.

 

[bstedh]

Just testing my ability to insert pics from my new device...

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[donptal]

Congratulations bstedh! Tuning in here for the final outcome. Keep it up guys!

 

[jrm850]

Hey Bstedh, There is a free PC based O-Scope that uses the sound card on your computer. It has limited functionality and is pretty slow, but it should work well enough to let you see your duty cycle. You'll have to solder some probes to a stereo jack and plug it into your mic socket on the PC. It's called Winscope.

Re: Duty cycle - Was that 220ohm resistor in series with your 500ohm pot? Did r2=150ohm? If so I am calculating a duty cycle of between 71% and 85%

 

[bstedh]

I will have to look into winscope.

I get pretty full range with the resistor setup in Clutch's diagram.
R1= 220
R2=150
Pot=200
I am also going to try his option of eliminating r2.

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[Java_Az]

I installed Xo scope for linux but have not tried it out yet. Need to find a old head set i can cut the wires off of.
xoscope for Linux
EDIT:The signals for the oscilloscope can be internal to the computer (MP3 player, function generator etc.) or from external sources (line-in, microphone). For external sources care has to be taken, not to exceed the voltage range of the inputs. The range is usually only ±0.7V !! If higher voltage need to be analyzed, a voltage divider has to be used. Additional protection diodes are recommended in order to avoid any damage to the sound card and to the computer.
This one kicks but. it is windows based but i am running it in wine. Nicest one i have found yet.
http://www.zeitnitz.de/Christian/scope_en

Here is a article with a guy reviewing the software
http://geekcircuits.com/2010/02/sound-card-oscilloscope/

 

[bstedh]

I installed Xo scope for linux but have not tried it out yet. Need to find a old head set i can cut the wires off of.
xoscope for Linux
EDIT: IF you try this out be sure to use a voltage divider so your not inputting more then 1.7volts into your sound card. More then 1.7 volts your going to fry it !!!!!!!!!
This one kicks but. it is windows based but i am running it in wine. Nicest one i have found yet.
http://www.zeitnitz.de/Christian/scope_en

Here is a article with a guy reviewing the software
http://geekcircuits.com/2010/02/sound-card-oscilloscope/

Holy crap, that last program has a function generator! Sound card triggered PWM fet off the power supply rail sounds like fun.

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[clutchjunkie]

here is my most recent soldered up circuit:

Almost exactly 1/2 the size of a AAA battery, using only through hole components. I am getting a lot better at soldering too, hard to see in the crap cameraphone pics but the solder joints are all smooth, clean, and only have solder where they should. Of course, I have been practicing, this is #5 of these I have made so far just with the 555 pwm circuit. That video Asnider posted gave me a few pointers, too, so thanks for that.

Something alse I stumbled across that I don't quite understand. I found that if you connect pin 6 and 7 and run that directly to the center leg of the potentiometer, with no diode, the circuit still works and gives me a decent range of about 2.8-5.5v under load (using a 500ohm pot and a 330 ohm resistor with a dual coil). The taste goes from really weak to burning, which is about right for that voltage range.

Which is why I am confused.

Everything I have read has said the diode is necessary to go under 50% duty cycle, yet here I am swinging around both sides of 50% with no diode and no problem. I am using fairchild semi's 555's, not that it should matter. If you guys have the same results, that would be great because that would eliminate yet another component and make everything even simpler.

 

[jrm850]

here is my most recent soldered up circuit:

Almost exactly 1/2 the size of a AAA battery, using only through hole components. I am getting a lot better at soldering too, hard to see in the crap cameraphone pics but the solder joints are all smooth, clean, and only have solder where they should. Of course, I have been practicing, this is #5 of these I have made so far just with the 555 pwm circuit. That video Asnider posted gave me a few pointers, too, so thanks for that.

Something alse I stumbled across that I don't quite understand. I found that if you connect pin 6 and 7 and run that directly to the center leg of the potentiometer, with no diode, the circuit still works and gives me a decent range of about 2.8-5.5v under load (using a 500ohm pot and a 330 ohm resistor with a dual coil). The taste goes from really weak to burning, which is about right for that voltage range.

Which is why I am confused.

Everything I have read has said the diode is necessary to go under 50% duty cycle, yet here I am swinging around both sides of 50% with no diode and no problem. I am using fairchild semi's 555's, not that it should matter. If you guys have the same results, that would be great because that would eliminate yet another component and make everything even simpler.

You can get full range duty cycle by using fixed resistors in the classic r1,r2 configuration. Set your pot up as a voltage divider connected to the ctl pin. You will get a large frequency range but it shouldn't matter for this application.

 

[jrm850]

This circuit should give full range duty cycle with minimal part count. You can recreate it using this applet - Circuit Simulator Applet - to see how it works.

 

[bstedh]

Java,
I just dropped a hand full of NFETs into the mail for ya.

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[bstedh]

Clutch,

Could you diagram your board layout for others to use. I am of course assuming you are using a proto board.

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[Java_Az]

Java,
I just dropped a hand full of NFETs into the mail for ya.

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Cool Deal Appreciate it.
Hows those boards going for you. 0603's are fun to solder, made a Digikey order today and i had to go with some 0402 on one part i needed. I hate to go that small but i didnt have a choice. I bought a lot of extras just in case some disappear into nevernever land on me.

Found this on a buffer for using the sound card as a scope. Buffer Hardware for xoscope Might just make a SMD.SMT version of it. Two probes on ebay shipped are about 11 bucks. Might just have to whip one up.

 

[bstedh]

I haven't had a chance to put my digikey order together yet. Too many irons in the fire at the moment. Hopefully I will get it done tonight or tomorrow.

By the way the nfets I sent are all similar or the same as the one I linked to earlier and have all been tested.

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[bstedh]

Playing around with my proto type is seems that a good rms voltage "LOADED" is between 2.5Vrms ~ 3.5Vrms. They seem to run way hotter with the PWM than a standard switching regulator at lower voltage. Or my cheap harbor freight meter may not be giving me accurate rms voltages =].

My idea for the lever type POT actuator will not work. There is too much difference in adjustment levels between different ohm carto's. I set my 3ohm carto to 3Vrms and it was working really hot. I left it at that setting and put a 2ohm DC on and the loaded voltage dropped to 2.5Vrms and was vaping good but cool.

I am going to un solder the 200 ohm pot and put the 500 ohm back on to see what difference that makes.

 

[bstedh]

I have a question that you guys might be able to answer. When looking at a circuit board the components usually have a reference label. R is for resistor, C is for capacitor, D for diode, Q for semiconductor... What does CR reference? They look like a diode or tantalum capacitor but I'm not sure what they are.