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  1. R

    sound patterns

    Hi, Many thanks for your help. Please could you explain how this works. Also is the slight overshoot of the pulse a characteristic of this circuit I.e. after the train of pulses has completed there is s delay before the pulse falls to 0V. What happens if the input was a flat line? Best...
  2. R

    sound patterns

    Hi, thanks for your input The other sound pattern is again 10ms short pulse at 3khz and then 10 sec delay of no pulses then back to 10ms pulse. The other pattern is 3 consecutive pulses of 10ms with a delay of 200ms in between. Please could you show me what you mean by retrievable...
  3. R

    sound patterns

    Hi All, I was wondering if someone could help me. I have a requirement to detect different sound patterns that drive a piezo buzzer. The sound patterns differ for different types of alarm. This is an automated system which h can be left running and then it keeps a record of alarms that have...
  4. R

    Buzzer Help

    Thanks. If I put 5mA through the sender, that should be ok? Would there be a problem with the differentiator part of the circuit, just to detect edges or is there a better way to achieve this? Best regards, Raj
  5. R

    Buzzer Help

    Hi, I have attached a copy of the voltge seen on a piezo buzzer. I need to ckamp this to 3V3 and then detect the edges of the waverform at 1.17 secs, feed this into a microcontroller and measure the time between pulses. I was thinking of clamping the wavefor which is 30V by using a suitable...
  6. R

    Understanding The Following Circuit

    Hi, This is my modified circur based on your observations. I have included the 10K resistor. you said 'Think of the 10 kΩ resistor and the MOSFET as two resistors connected in series between -5 V and ground, the junction of the two being a voltage divider connected to pin 2. As the MOSFET is...
  7. R

    Understanding The Following Circuit

    I think having the circuit as it is with the 10K resistor to -5V might be the easiest option, I think. As you say in your explanation, This can then provide a negative current through the 1M resistor. The 1M can go to one input of the CO sensor and the other end of the CO sensor to 0V. I will...
  8. R

    Understanding The Following Circuit

    Hi, Many thanks for your much valued input and time in helping me solve this problem. The purpose of this circuit is to simulate CO levels, that can be varied by adjusting the PSU voltage output. In the end the PSU will be replaced by a DAC. A voltage output on the DAC will produce a negative...
  9. R

    Understanding The Following Circuit

    Hi thanks very much for taking time to look at the circuit. If I put a 10K resistor from pin 2 the other end to -5V, would this be another way around the problem. Then negative current could flow through the 1M resistor then to one end of my co sensor, the other end connected to 0V? I am not...
  10. R

    Understanding The Following Circuit

    Hi, pin3 is connected to a negative supply. Pin2 is connected to the input of a Carbon Monoxide sensor, which needs a negative current. The idea being the pin3 of the opamp is the reference, the FET keeps pin 2 at same potential as pin3 of the opamp. Then the resistor at pin2 (which is a 10K)...
  11. R

    Understanding The Following Circuit

    Hi, thanks for your help. The circuit is to generate a negative current, so the o/p is an I/p as you correctly say. My understanding was that whatever we have at +Vin , we see at -Vin, due to the source at the same potential ie. Clamps it at that voltage. So do we then get a potentiometer...
  12. R

    Understanding The Following Circuit

    Hi All, I was wondering if someone can help me understand the attached circuit. this is what i have measured:- Input to the opamp is -0.5V (from a PSU), because of feedback the inverting terminal must be at the same potential ie -0.5V because of virtual earth of opamp. The gate of the FET is...
  13. R

    LED monitor using phototransistor

    Hi, thanks for your help so far. much appreciared. i am not 100% sure on the uv and visible light scenario, but the led is red and the other is green. could i not use a uv phototransistor with these? what would happen if i did? i am looking to power the led via 3v3 supply and resistor. the...
  14. R

    LED monitor using phototransistor

    Hi, The LED will need to be monitored as part of tests, that could be 24-72 hours long, we are checking when it illuminates. So hence need to be an automated system. The LED(s) is red, current is 15mA. I intend to build a small PCB which will have the phototransistor circuitry on, this will then...
  15. R

    LED monitor using phototransistor

    Hi all, I have a requirement to monitor a LED using a photo transistor. The LED is powered from a 3V3 supply via a resistor, the cathode if the LED is going to a I/O line of a micro. So a logic 1 keeps the LED off and a logic 0 lights the LED. If I use a phototransistor, do I need to match the...
  16. R

    op amp question

    Thanks Bob.
  17. R

    op amp question

    Hi all, I have a op amp circuit powered from +5V and -5V supply rails. If the non inverting input is sitting at 1V. If I now put a -2V on the inverting input. Should the output still go negative. Sorry this has been puzzling me. Best regards, Raj
  18. R

    detecting low voltage with PIC

    Thankyou Bob. It seems to make sense.
  19. R

    pull down resistor for npn relay driver

    Thanks ak. Just a final question. I have never really understood the meaning of high impedance or low impedance. What do they actually mean in real terms and why are they so important when connecting circuit outputs to circuit inputs. Is it loading effects? Any help would be much appreciated...
  20. R

    detecting low voltage with PIC

    Thanks Bob. Is the 1K only used to limit current? Similarly I am not sure on the understanding of the 330R, why this value for longer cables?
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