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  1. K

    I'm back - a new circuit for the mini-golf course

    Do you have a pic of the original boards? I'm curious as to what's on them. I 2nd the suggestion for a SR (aka bistable) flip flop. Another option is a relay wired to latch itself: have the 5V pulse from the sensor energize a relay, and then the relay contacts themselves keep the relay (and...
  2. K

    Display cabinet - PIR motion sensor & LED lights

    Measure the current draw of the circuit when idle (LEDs off) and again with them illuminated with fresh batteries. Based on that we can estimate the lifespan of a set of AAs (average around 2000 mAH for a set of alkalines) Another factor to consider is the voltage of the batteries will drop as...
  3. K

    Display cabinet - PIR motion sensor & LED lights

    My guess is the PIR sensor can only put out a small amount of current. Measure the voltage between the PIR output and ground (-) with it left open (disconnected from the transistor) and also with it connected. Does the voltage drop dramatically when it's supplying a current? I found a...
  4. K

    help over microcontroller code

    Strings are arrays of chars, so that's what I was referring to. But in the original code, i wasn't used for anything so initializing and incrementing it would have been a waste. In XC8 for PIC at least, pointers add overhead since they could point to any number of things: variables in memory...
  5. K

    help over microcontroller code

    I was going to point that out, but I figured I'd leave it out for simplicity's sake for now. It could have been done with: "for(;*cmd!='\0';cmd++)" as well. Also, depending on the micro, pointers may be less efficient than using arrays (lower-end PICs come to mind). Using " for(i=0; cmd[ i ]...
  6. K

    help over microcontroller code

    Here's a commented version of the above program: void gsmcmdsend(unsigned char *cmd); unsigned char gsm_cmd3[]="AT&W"; // GSM modem commands unsigned char gsm_cmd4[]="AT+CMGF"; void gsmcmdsend(unsigned char *cmd) { unsigned char i; for(i=0;*cmd!='\0';i++) // Loop through command one...
  7. K

    What is this part?

    I've never heard of a Xxxxxxxxxx before. Had to look it up, but that's what it looks like after looking at pics of them on the 'net. (and we all thought the interwebs was just for p0rn! lol) Now for the real question: does it still work? I wonder what the lifespan of a Xxxxxxxxxxxx is...
  8. K

    Fast, high current switching

    The internal clock will be less accurate than the crystal, but unless you need precise timing of your solenoid pulses that won't matter. Is the Arduino doing anything other than supplying a signal to the solenoid? Is it varying the frequency based on certain inputs? Is it providing outputs to...
  9. K

    Fast, high current switching

    The 10K resistor goes between the gate and the source (ground), not to 12V. The way you show it the FET will always be on, not what you want. Its purpose is to discharge the gate charge when the optocoupler turns off, so the FET turns off as well. You may not need the 10-ohm resistor. It...
  10. K

    LED optic sensor circuit

    I wouldn't worry about the 800mV. The closer to 0V you can get while illuminated/unblocked, and the closer to 5V while unilluminated/blocked the better. Assuming the input circuit is a Schmitt trigger digital input, the low threshold is probably ~1V and the high threshold somewhere in the 3-4V...
  11. K

    LED optic sensor circuit

    Ok, I thought you were referencing the phototransistor the OP purchased on his last trip to RadioShack (post #39). I think he's planning to use that instead of the photodiode + 2n3904 circuit, and from what I've seen on the website it's a 2-leaded part with no base lead. Sensitivity can be...
  12. K

    LED optic sensor circuit

    That'll work if the base lead is available on the phototransistor. I don't think it is on the RadioShack one. It's just a 2-lead T1 3/4 case similar to an LED. In any case, it should work "as-is". A lower voltage drop gives a larger margin of error. You can use a higher value resistor to...
  13. K

    LED optic sensor circuit

    Another way to see if it's a photodiode or phototransistor is to test it with the diode-test function on your meter, without light shining on it (put a piece of dark tape over it). It'll conduct in the forward direction with a typical diode voltage drop but not the reverse direction if it is a...
  14. K

    LED optic sensor circuit

    What voltage and resistor value are you driving the LED with? IR LEDs have a lower voltage drop (1.2V typical) and a higher current rating than visible LEDs. Some can handle 100 mA, though I recommend keeping it below 30-40 mA for maximum life. The sensor is working as you want (other than it...
  15. K

    LED optic sensor circuit

    Does your Sony video camera have a "nightshot" mode? If it does, use that mode, and cover over the IR light on the camera. You should see the LED light with that. When you tested the LED, you used a resistor in series, right? If you didn't, you could have blown it. Try reverse biasing the...
  16. K

    LED optic sensor circuit

    I've used those combo packs from RadioShack and IIRC the tinted one is the LED and the clear one is the sensor, which is actually a photodiode, not a phototransistor. While all camera sensors can "see" IR, some cameras have IR filters in the lens that prevent them from responding to IR light...
  17. K

    Unknown Piece of Electrical Equipment?

    Just a guess, but some sort of light controller/dimmer?
  18. K

    Write Only Memory (WOM)

    I have one in my brain. Information goes in, never to be seen again....
  19. K

    Write Only Memory (WOM)

    That datasheet was written as a joke. Look at it closely, especially the footnotes. Think about it: what's the point of a memory that can be written to but not read back?
  20. K

    iPod as oscillator for scope wave learning?

    It may be easier to buy a stereo mini-plug with solder lugs and attach thicker wires to that instead of using headphone wires which are tiny. Then you can plug it into your iPod or other device and not have to worry about shorting things out or getting the connections wrong.
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