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  1. darrins

    Guitar Amplifier

    Sorry about the links to tube amps. :-[ I just did got these links from a google search and didn't read all the content. You may be able to find a good amp on eBay. Sometimes it's cheaper to buy than build. I certainly got a good deal on my oscilloscope. Not that I could build an...
  2. darrins

    Guitar Amplifier

    Try these sites: http://www.ax84.com/home.html http://freespace.virgin.net/vyse.co/build_your_own_amp.htm http://www.duncanamps.com/brewlink_amps.html Good luck. :) Darrin
  3. darrins

    Differential amplifier question

    Thanks. I'll add it to my collection. ;D
  4. darrins

    Differential amplifier question

    Ante, Funny you should post that. I just downloaded the same paper yesterday, but the one you posted looks more recent. I guess I need to stop being lazy and just read it. :-[ Looks like a good paper from what I've read so far. Thanks. Darrin
  5. darrins

    Differential amplifier question

    I have a couple of basic questions related to a differential amplifiers. If these types of questions are better suited to the Theory Articles board, please let me know. :) I want to amplify the voltage difference between a sensor (Vs) and a reference voltage (Vref). I only want to amplify...
  6. darrins

    NEWB HERE!

    Unfortunately, all the really good books are also big books. Try "The Art of Electronics" by Paul Horowitz and Winfield Hill. Or "Practical Electronics for Inventors" by Paul Scherz.
  7. darrins

    PWM using 555 timer

    Ante, Just to clarify, I know I'm not controlling the phase angle of the triac. I'm simply turning the triac on and off for short periods of time. More heat needed -- longer "ON" time (and vice versa). I suppose the low frequency is needed to ensure you get some zero crossing with the AC...
  8. darrins

    Whoops!

    I did that once when I was really tired. I put my oscilloscope probes across the AC mains on a power supply and POOF, one of my probes got shortened by 2mm. Also scortched a nearby cap. At least the fuse did what it was supposed to do. My scope was unharmed.
  9. darrins

    PWM using 555 timer

    audioguru, This is how I got confused in the first place. I want to control the phase angle to the triac so I can controll how much power is delivered to my heater. The first circuit I built uses a heat sensor, a comparator, and a standard light dimmer switch. When my temp sensor is below...
  10. darrins

    PWM using 555 timer

    Thanks Ante and audioguru. I will try experimenting with a few different designs, including the one Ante simulated. I think I will also try stuffing a few of my temperature sensors (LM34) in a copper tube and use a summing amplifier to calculate an average temperature. A lot of the temp...
  11. darrins

    Shut off devices by eletromagnetic waves.

    Ante, Looks like that site has been shut down. :( Darrin
  12. darrins

    PWM using 555 timer

    Ante and audioguru, Just found another interesting circuit. This one is from http://home.cogeco.ca/~rpaisley4/LM555.html#7 This circuit looks like it might be a little easier to predict and the pulse width can be between 5% and 95% of nominal.
  13. darrins

    PWM using 555 timer

    Ante and audioguru, The voltage difference between my heat sensor and reference will be, at most, around 300 mA. I've read that, as a rule-of-thumb, that the control voltage at pin 5 should be between 45% and 90% of Vcc. Obviously, I'll have to amplify my signal if I'm going to use a Vcc of...
  14. darrins

    PWM using 555 timer

    Ante, Cool. It worked!!! 8) This will help me greatly. :D Modeling and simulation are great time savers (not to mention money). Thanks again. Darrin
  15. darrins

    PWM using 555 timer

    Ante, I downloaded the shareware version of Proteus (Proteus 6 Lite). Would it allow me to simulate this circuit? I don't know how to use the program, but I'm sure I could learn. Heck, I used SPICE in college (pre-Windows days). Is it possible for Proteus lite to load the model you have...
  16. darrins

    PWM using 555 timer

    I found a circuit that is very close to what I am trying to do: This is from http://www.saburchill.com/tech/electronics/elect039.html This circuit uses a sound sensor to vary the brightness of a lightbulb. I also figured out some timing formulas based on threshold voltage (Vth) and...
  17. darrins

    PWM using 555 timer

    I found a website that describes using the 555 as a voltage controlled oscillator. http://www.analog.com/library/analogDialogue/archives/29-3/single.html At the bottom of the page, they have a formula for output frequency. Charge time, Tc = (R5 + R6)*C5 * ln [ (1-Vin/6.8V) / (1-Vin/3.4V) ]...
  18. darrins

    PWM using 555 timer

    Thanks for the advice guys. I read in one of my textbooks that the control voltage affects the reference voltages of the IC's internal comparators (normally 2/3 and 1/3 of Vcc), but it doesn't say exactly what this effect is. Here's what is said about pin 5 on Tony van Roon's tutorial page...
  19. darrins

    PWM using 555 timer

    I read several datasheets and application notes on 555 timers, but I can't seem to find the information I'm looking for. Specifically, I'd like to use the 555 as a pulse width modulator by using the control voltage (pin 5). The datasheets indicate that in monostable mode, the output pulse...
  20. darrins

    Mini golf cart from UPS batteries

    I think those batteries are toast. I'll send them someplace to be recycled. There's still a lot of other useful parts in the UPS, so it wasn't a total waste. It has a gigantic transformer in it. I don't know what I'll use that for -- maybe a boat anchor. Cheers. Darrin
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