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  1. C

    HELP NEEDED

    Count the cycles of a precise 1Mhz oscillator during one cycle of your input waveform. Are you sure you don't want to use a microcontroller?
  2. C

    HELP NEEDED

    One way to ignore higher-than-fundamental harmonics is with hysteresis. In the picture you can see an input waveform with multiple peaks, and two levels A and B. When determining a rising edge in the input, we compare with level A - we assume the cycle starts when the waveform is determined to...
  3. C

    LED dimmer

    Here's the last version of this that I'm going to do. At the top left is a nearly-trianglular waveform generator. The peak and trough voltages are carefully chosen. The bottom left part is the ramp generator. I decided to be careful here because the level limits are important, given the range...
  4. C

    Paralell resistors

    No. I said sorry because I had just realised I repeated exactly what you said.
  5. C

    LED dimmer

    Ugly, and incomplete, but hey, it's a work in progress! This was the test circuit I messed around with. The biggest trouble with it is my opamp's limited output swing, making levels difficult to predict, and making it complicated to switch the transistor. Amongst other things.
  6. C

    LED dimmer

    Well, I've made the PWM version, and guess what - the apparent rate of brightening and dimming is very similar to the circuit I posted before, which makes me wonder - does the eye perceive brightness in the same way the ear perceives volume? If so the relationship would be non-linear (perhaps...
  7. C

    LED dimmer

    In the picture, the blue sawtooth waveform is generated by an oscillator. 1kHz should be fine. The red signal is a ramp generated when you press the switch. When the switch is released, the ramp would rise instead of fall. The green waveform is generated by comparing the blue and red - when the...
  8. C

    LED dimmer

    That transistor is a limiting factor, for sure, but what Theatronics and I proposed was a PWM design which would not only make the on/off change smoother visually, but would also vastly improve the power efficiency, so heat (brute force) wouldn't be such an issue. The trick is to have that...
  9. C

    LED dimmer

    PDMAX is the maximum power it can dissipate when cold. Since it's likely to heat up for a few seconds as the lights come on and off, You are more interested in the maximum it can dissipate without a heatsink, in air at 25 degrees C. This figure is quoted as "PC(Ta=25)". A good transistor for up...
  10. C

    Scopes

    I used a Goldstar CRT scope for years, and then changed to an Tektronix LCD. The CRT is clearer, and there's something about analogue that's just plain sweet. However, now I'm used to the digital scope, I wouldn't go back for all the money in the world. It's just great. Of course, if you really...
  11. C

    Paralell resistors

    I believe you are confused because you stated that two 50 Ohm resistors in parallel causes them to become 25 Ohms each. This is incorrect. They stay 50 Ohms each, but the resistance of the whole becomes 25 Ohms. A single water pipe has a certain resistance to flow, but two such pipes permit...
  12. C

    LED dimmer

    Sorry, max power will be about half supply voltage multiplied by half max current, like this: (12V / 2) * (160mA / 2) = 0.48W
  13. C

    LED dimmer

    Yes, you can connect as many resistor/LED pairs as you like, limited only by the current and power rating of Q2. At full brightness each resistor will have about 10V across it (12V supply - 2V across diode). Use Ohm's law to work out the resistance and current for each LED. Knowing the current...
  14. C

    LED dimmer

    You could pull out Q1 and connect Q2's base where Q1's base used to be (betwen R1 and R2). This might work - though if it does the ramp probably won't be very linear, and the lighting and dimming not very smooth. Try it! As for the LEDs being always lit, they won't if Q2 isn't conducting. The...
  15. C

    LED dimmer

    Hey Theatronics. That's what I said. PWM. So that's what I did. But it's two transistors, a comparator, two caps and half a dozen resistors. I think one could wrestle a 555 into doing this, too. Slackjack wants simple, so I'll leave it at that. I was thinking of another way though, which...
  16. C

    LED dimmer

    I can't imagine a way of causing the lights to slowly dim AND slowly light without the use of a huge capacitor (or two - each 20000uF or more) and a double pole switch. Even then the initial charge/discharge rate of the capacitors will be high, dropping off with time, meaning there won't be a...
  17. C

    LED dimmer

    Here's one I knocked up. The trouble with LEDs is that their apparent brightness does not change linearly with current, so this design might not be as smooth as you want. But it works. It's a ramp generator - press the switch and the voltage at Q2's collector slowly and linearly drops...
  18. C

    Thinking about getting into electronics??

    Fifteen years ago I was fixing PCs with an oscilloscope, logic analyser and a solder station. Fantastic! These days one almost never gets to use more than a screwdriver. Hobby electronics seems to be the only place to use the knowledge I have. So now I work with horses instead, which have an...
  19. C

    Interfacing circuits to the PC

    Before you make your decision about what port to use, check this out: http://www.sparkfun.com/commerce/product_info.php?products_id=762 This "Bit Whacker" looks perfect for simple and modern interfacing with any USB equipped computer! On plug-and-play USB systems it identifies itself as a...
  20. C

    Beginner's Question

    Different kinds of IC technology use different kinds of transistors. TTL ICs, such as the 7400 series, use bipolar junction transistors (BJT). CMOS ICs, such as the 4000 series logic chips, use field effect transistors (FET). Generally, each stage in a logic circuit has an output section...
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