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  1. R

    Reaction Game

    Hi All, I need a bit if advise. I am designing a childs reaction game. there are 4 LEDS and push-button type switches. The LEDs will light uo randomly and the children will hit the key relating to the lit LED. This will be done with a PIC micro and written in C. What would be the best way...
  2. R

    Floating current source

    If you can imagine a 3V battery with a 1M resistor connected in series. This give 3uA current. If I connect the battery terminal ends to the UUT, this then gives me an alarm a CO alarm. The requirement is to have a constant current source not referenced to 0V but floating as the battery and...
  3. R

    Floating current source

    Hi all, Thanks for your help. The PCB was designed with the circuit as shown. Then 6 months later the requirement for a floating current source was required. Hence the problem of keeping the mods to a minimum. At the moment the input opamp is controlled by an adjustable voltage at its input...
  4. R

    Floating current source

    No it doesn't. Just a typo. So I canake this into a floating current source by just changing the supplies to the opamp? i.e. using separate supply or battery powered as mentioned by hevans1944? The control voltage for the first opamp is fed from an adjustable supply. The second opamp keeps the...
  5. R

    Floating current source

    The current control needs to be accurate. Tolerance acceptable would be around ,10%.
  6. R

    Floating current source

    The existing supply is not isolated. The unit is powered from a PSU which gives out +12/-12V and 5V. The 5V generates 3V3 from a LDO. The -12V generates a -5V from a LDO. The +5/-5V supply the opamp. These are all DC voltages from a PSU which is fed from mains. Floating for me means something...
  7. R

    Floating current source

    Hi Alec_t, Please could you elaborate? Am I not sure on how to connect the opto device to this circuit. I am looking at minimising the circuitry modifications. Would I need to use a seperate supply for the opto device? Also would the opto dark current need to be very low as i am looking at very...
  8. R

    Floating current source

    Hi all, I have the following circuit (see attached image). What would be the best way fro me to make the output a floating current source rather than with ground connection? Or use a current transformer? Note I am using currents of 100nA-300uA. Is this possible? Or could I use a photovoltaic...
  9. R

    Python Rs232

    Thanks. I have also cone across PyVisa, this I believe are a set of libraries for instrument control such as RS232, GBIP etc. Not sure if they have libraries for my multimeter.
  10. R

    long wires on digital signal

    Thanks
  11. R

    Making It High Impedance

    Thank you very much.
  12. R

    long wires on digital signal

    Thanks Harald. What would be the best way to attenuate, a potential divider?
  13. R

    Making It High Impedance

    This is my confusion. The output enable line needs to be a high at switch on, hence the pull up. Now I thought that internally the i/O line has a transistor. The pull up is from the transistor collector to Vcc. Now for me to switch this line 0, don't I just output a 1, si the internal transistor...
  14. R

    Python Rs232

    Hi all, I am using python to control a digital multimeter through rs232. I have mages to send the Meyer commands from real term, so I can read the I'd number, read the software version, measure current etc. This works fine. I want to expand this so I can read and measure from the Meyer nut use...
  15. R

    Help With Circuit

    Hi Steve, Some further help is required. What would be the easiest way to modify this circuit to meet the following requirements: 1. To have a positive constant current 2. To make this current source floating I.e. no ground connection on output side 1. Use n channel FETwith connection reversed...
  16. R

    long wires on digital signal

    Hi, I am driving a PWM circuit and low pass filter from a microcontroller. The output from this circuit will have a voltage in the range of 5-15mV. However there is a cable (twisted pair with overall screen) between the microcontroller and this PWM circuitry. The cable is around 12-18 inches...
  17. R

    Making It High Impedance

    Thanks. Then to bring it low, it's a simple case of outputting a 1 on the I/O line. The internal transistor (with its collector to Vcc via 10K) will pull the output to OV. Does that sound reasonable?
  18. R

    micro I/o lines

    Hi all, I need to understand micro I/o lines for a PIC 18F. If I put a 10k pull up on a pin, and configure the pin as a input. It will read high. But if the same pin is set to an output, what happens? Also can I drive this low even though it has a pull up, by this I mean using the internal FET...
  19. R

    Making It High Impedance

    Thanks Bob. Please I need to ask another question. If I tie the output enable high via a 10k pull up to vcc. Do I need to configure the pin as a output? After the initial micro power up sequence, this line then needs to be brought low so I can operate the shift register. Without using a...
  20. R

    Making It High Impedance

    Hi all, I have a shift register 74hc595. This is driving a uln2003lv transistor array, that in turn drive relay coils. The shift register is controlled by a microcontroller. I need to make sure that the shift register is high z on switch on si I don't get relays coming on. From the truth table...
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