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  1. KrisBlueNZ

    Possible Project??

    Between 100 ohms and 10 kilohms should be fine.
  2. KrisBlueNZ

    Possible Project??

    Yes, RSA and RSB should be within ±15% of the IDEAL or NOMINAL resistance of their respective circuits. Yes, you can make a connector with fixed resistors, to give you a battery check. You could also include fixed resistors on the board, switched with a double-pole pushbutton. These won't give...
  3. KrisBlueNZ

    Possible Project??

    If one resistance, or both resistances, are out of spec, then you'll see a red indication, which is important when you're doing boring bulk testing. The test operator could overlook a missing green indication, which is why I think the red LEDs are important. Of course, he could also overlook a...
  4. KrisBlueNZ

    Possible Project??

    Not true! If both resistances are open circuit, there will be a clear indication: the LEDs will not light at all. Two green indications mean the test passed; anything else means fail. I guess I should have spelled that out. Whether a separate push-to-test button is appropriate depends on how...
  5. KrisBlueNZ

    Help Needed with SCR and Optocoupler

    Adam, yes, a bleed resistor is a good idea. For two 1W resistors in series, running at half their rated dissipation, each resistor should be about 68k. It will take about 20 minutes to discharge a 3000 µF capacitance to a safe voltage (30V DC). Adam, do you know what polarity the trigger...
  6. KrisBlueNZ

    Possible Project??

    Here's a design that should do what you want. It runs from a 9V PP3-type battery and it's designed for low current consumption (about 20 µA or 200 µW) when nothing is plugged into the test connector, so an Alkaline battery should last at least two years, and it doesn't need an ON/OFF...
  7. KrisBlueNZ

    Help Needed with SCR and Optocoupler

    The OP's circuit will still cause gate-to-cathode current to flow when the optocoupler conducts. It uses the voltage that already exists across the SCR to feed current into the gate. There's no real difference between his circuit and mine; the fact that my circuit has the gate connected to the...
  8. KrisBlueNZ

    Converter Circuit

    The resistor suggested by Laplace does exactly what you asked for. If you want something different, you'll have to be A LOT MORE SPECIFIC about your requirements.
  9. KrisBlueNZ

    Help Needed with SCR and Optocoupler

    I don't see any definite problems with your circuit that would prevent it from working. I have drawn up your design with a few suggested changes that you can try. Normally when an SCR drives a trigger transformer, the SCR is connected with its cathode to the negative rail, for tidiness. The...
  10. KrisBlueNZ

    Possible Project??

    What do you mean about temperature sensing? Are you saying that the resistance of the device under test is supposed to vary depending on temperature? If so, you'll need to define the relationship.
  11. KrisBlueNZ

    pic programming help - controlling GSM to send message from PIC16F873A

    That looks right. I agree with Richard's suggestion: feed the RS-232 transmitted data into the received data connection of a serial port on a PC and run some terminal software on the PC. Set it to 9600 baud and see whether it receives the transmission from the PIC. You can also use an...
  12. KrisBlueNZ

    pic programming help - controlling GSM to send message from PIC16F873A

    That's right, but it's not a complete diagram. Most of the detail is missing. Pin numbers, for example. Also you haven't connected the data in the other direction. Even if it isn't needed (yet), you should connect it.
  13. KrisBlueNZ

    pic programming help - controlling GSM to send message from PIC16F873A

    Yes. Post a schematic of what you have done.
  14. KrisBlueNZ

    pic programming help - controlling GSM to send message from PIC16F873A

    PIC TXD -----> (T.IN) MAX232 transmitter (T.OUT) -----> GSM "TXD" connection PIC RXD <----- (R.OUT) MAX232 receiver (R.IN) <----- GSM "RXD" connection The GSM modem, being a DCE (data communications equipment) component in the RS-232 conventions, should actually receive its data on the...
  15. KrisBlueNZ

    Code causes error report from PIC CCS compiler

    Did you fix the delay_ms() problem that was causing the compiler to report an error as shown in post #5? Does your code compile properly now? What is the symptom of the problem? In other words, what does the code not do that it should do?
  16. KrisBlueNZ

    pic programming help - controlling GSM to send message from PIC16F873A

    The GSM modem probably does have a MAX232 inside it, to convert its internal logic-level signals to RS-232 levels. You need ANOTHER MAX232, on your board, to convert the RS-232-level signals back to logic levels that you can connect to your PIC.
  17. KrisBlueNZ

    Help designing circuit for box alert light

    I've updated the diagram to use a normally closed pushbutton. That is, a pushbutton that has continuity when there is no force pushing it down. When the box lid is down, it pushes the pushbutton down, and breaks the circuit. When the box lid is lifted, the pushbutton springs up and closes the...
  18. KrisBlueNZ

    Automated Sliding Door

    Interesting. You've connected the relay coils straight across the timer outputs. So the timer must provide voltage on its output when it's activated. That's different from the usual arrangement - normally the output is just a relay contact that closes to complete an external circuit. The...
  19. KrisBlueNZ

    Help designing circuit for box alert light

    Here's my suggestion. It's very similar to yours, Steve. Here's a circuit description for the OP. U1 is a CD40106B hex Schmitt trigger inverter IC. It is shown as six gates named U1A~U1F. Power is connected to pins 14 and 7, which are shown on the first gate. CD is a "decoupling" capacitor...
  20. KrisBlueNZ

    pic programming help - controlling GSM to send message from PIC16F873A

    OK, as gorgon says, if the GSM modem connects directly to a COM port, you need an RS-232 transceiver IC between the PIC and the GSM modem to convert between logic levels and RS-232 levels. The transceiver also inverts the signals - transmitters convert logic low to positive voltage, and logic...
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