Search results

Search Forums New Posts
  1. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    The specifications for that GSM module are very clear: 4.5~5.5V supply required... You should have actual pull-up and pull-down resistors on the board. The PIC's pins probably go high-impedance while it's resetting. Good! You've written a fair bit of code then? That's a nice little chip. It's...
  2. KrisBlueNZ

    AT89S52 vs ATmega644

    Correct.
  3. KrisBlueNZ

    AT89S52 vs ATmega644

    The AT89S52 uses the 8051 architecture; the ATMeega644 uses the AVR architecture. They're fundamentally different and not code-compatible.
  4. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    I've had a look at the PIC16F628A data sheet. I think you can do it all without interrupts. Here's the architecture I suggest. Have a loop that runs constantly and calls separate functions for the various functions required: - Serial reception - poll RCIF bit to detect new data; store into a...
  5. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    Protection circuitry is for protection. You're not supposed to use it to control the normal charging process. Chargers use carefully determined algorithms and voltage, current and temperature sensing to charge the battery to optimise safety, performance and battery lifetime. Several...
  6. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    If you want to run the circuit while the battery is charging, it's best to power the circuit from a power supply and charge the battery through a separate path. If you don't do it that way, and a call comes in while the battery is being charged, your circuit will draw current from the charger...
  7. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    I don't see any output current rating given for those boards. It needs to be able to supply 2A peak for the GSM board. Also, looking at the schematic (which has multiple errors anyway), I see that the negative connections on the input and output are not common; they're interrupted by two...
  8. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    OK. Thanks for the link. There's not much information on it, is there. I noticed it needs a 5V supply. Are you using a separate battery for that? I see, RI is only available on pin 4 of the SIM900 IC itself. That's a good reason to use serial data instead. No, MOSFETs and bipolar transistors...
  9. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    Right. Seems like it would be simpler to just watch the ring indicator from the modem... assuming it's used. The modem may or may not drive that pin; you'll have to read the documentation or try it out to find out for sure. There's no difference. A loop that polls the state of an I/O pin...
  10. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    Right, you had it backwards. An N-channel MOSFET is comparable to an NPN bipolar transistor, and a P-channel MOSFET is comparable to a PNP. But MOSFETs are voltage-controlled, not current-controlled. Polarities and directions of arrows are all reversed for a P-channel MOSFET or PNP transistor...
  11. KrisBlueNZ

    Blowing fuses on 1980's Fisher CA-880

    As Duke said, you need to measure the voltage on the left channel speaker output. I would do it slightly differently: replace the fuse (again), disconnect the speaker, power it up, and measure the DC voltage across the speaker connections. If it's a direct coupled output stage, most likely one...
  12. KrisBlueNZ

    Toshiba CRT TV Model 21S1ES- No picture

    He said in his first post that TV channels are received with audio but no picture, so using the RF modulator inside a VCR will not help.
  13. KrisBlueNZ

    need help with simple 3v to 34v transistor relay/switch

    Not quite. The MOSFET should be in the +3.7V feed to the boost converter. Connect the boost converter's negative rail to your circuit's main negative rail. Connect the MOSFET with its source to +3.7V and its drain to the positive supply input connection of the boost converter. You could also...
  14. KrisBlueNZ

    Capacitor Value issues (simple)

    That's OK, I get the idea. It's impossible to say for sure. I think it's probably 12 uF but I think you should try to borrow a capacitance meter. Perhaps take your capacitor into a shop that sells multimeters and ask them if they'll measure it for you. That might work here. I don't know how...
  15. KrisBlueNZ

    Phototransistor latch circuit?

    OK, in that case the signal from the phototransistor will be very clean and you won't need a capacitor.
  16. KrisBlueNZ

    Phototransistor latch circuit?

    If you set the pot resistance to a low value, you will need more light on the phototransistor to activate the 555's output. That's the purpose of the pot. It sets the light sensitivity. You decide how much light you want to be the minimum brightness that's guaranteed to activate the output...
  17. KrisBlueNZ

    To shunt or not to shunt?

    The specs say that the measurement range is 0~20 mA. The power supply current is specified as 100 mA maximum. You need to use a 5V regulator connected to your 9V battery, to produce a 5V supply rail for your meter. You do not need a 470 ohm resistor. Have a look at the 78L05 data sheet...
  18. KrisBlueNZ

    Phototransistor latch circuit?

    That's kind of like asking "how long is a piece of string". If your light source is a fluorescent light that flickers 100 or 120 times per second, you'll need to add significant capacitance (e.g. 0.1 uF or more) to prevent multiple clocking. That capacitance works by delaying the change in the...
  19. KrisBlueNZ

    Two-coil latching relay arrangement

    Yes Duke, that's a discussion we had on an old thread: https://www.electronicspoint.com/problems-substituting-relay-t250057.html I prefer the bridge design because both halves of the mains cycle are used, so C1 can be half the size of the other option. This saves more money and space than you...
  20. KrisBlueNZ

    Phototransistor latch circuit?

    Yes. I suggested adding the capacitor only if you get unreliable clocking because the light source isn't steady, for example.
Top