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  1. KrisBlueNZ

    Constant current Source clarification

    The op-amp's inverting input is connected to the wrong place in the circuit. Assuming R1 is the shunt resistor and R3 is the load resistor, you need to connect the inverting input to Q1's source, i.e. the bottom end of R1, and connect the top end of R1 to the positive supply. This circuit won't...
  2. KrisBlueNZ

    IRF640 vs IRF640N

    Hi Jorge and welcome to Electronics Point :-) What brand are the existing devices? Is there a manufacturer's logo? See https://www.electronicspoint.com/resources/logos-for-electronic-component-manufacturers.47/ Have you downloaded the data sheet and tried to figure out what the N suffix means?
  3. KrisBlueNZ

    4~20 mA current generator

    No, DACs don't need to be programmed. You provide a reference voltage, and a digital representation of the output voltage you want, and it produces a voltage that you can feed to your voltage-to-current converter circuit. You can't find an 8-bit DAC with a single output? Did you look at the...
  4. KrisBlueNZ

    Can you identify this 14-pin IC in tone detector circuit from the schematic?

    It was a long time ago and he's forgotten. Now he's lost the data sheet.
  5. KrisBlueNZ

    Help calculating combined size of holes in a pipe

    I went via millimetres, and got the same result: 0.559 inches diameter.
  6. KrisBlueNZ

    Can you identify this 14-pin IC in tone detector circuit from the schematic?

    OK, I've made it less misleading! OK. Well, those comments could be a useful hint as well. A CD4046 wouldn't do that. BTW, what are the frequencies? Bummer!
  7. KrisBlueNZ

    Can you identify this 14-pin IC in tone detector circuit from the schematic?

    Ah, I see what you mean now. No, I don't recognise it, sorry. What is the power supply voltage? Perhaps someone will come across this thread later and recognise the device. I'll update the subject to make it more enticing.
  8. KrisBlueNZ

    Stage Line 500W amp repair project

    I don't think it's D38. What's the story with R117? I think I'm onto something there! Don't keep me in suspenders :-) Here's how Q46's base circuit is supposed to work. Initially assuming that Q46 isn't present. Voltage is applied across the string of three components - D38, R117 and R108, and...
  9. KrisBlueNZ

    Stage Line 500W amp repair project

    Yes, you're exactly right. Current through D38 and R117 is supposed to produce a voltage drop across R108, which is supposed to bias Q46 ON so it feeds +45V from its emitter to its collector. So you've confirmed that if Q46 was turning ON, the fault LED would go out. We need to find out why it's...
  10. KrisBlueNZ

    Can you identify this 14-pin IC in tone detector circuit from the schematic?

    It's hard to say without a schematic of how it's used. It could just be a gate IC being used as a phase comparator, or a monostable, or something like that. Or it could be a microcontroller with an internal clock oscillator. Show us a schematic of that part of the circuit, including the power...
  11. KrisBlueNZ

    4~20 mA current generator

    I don't think your instructor should be asking you to design a circuit if you haven't learned how! That circuit is not what I was thinking of, but since your instructor was so vague, he should accept that circuit as an answer. You're right that that circuit can't drive 4~20 mA through any load...
  12. KrisBlueNZ

    Help calculating combined size of holes in a pipe

    What do you mean "the single hole equivalent"? Do you mean a hole with the same area? In that case you need to calculate the area of each hole, multiply by 20, and convert that area back into a diameter. Area of a circle is pi r2 IIRC! BTW I've fixed your thread subject. "Heeeeeelp!" isn't very...
  13. KrisBlueNZ

    Looking for schematic for Digitech RDS1900

    Hello Ignacio and welcome to Electronics Point. I have fixed your post. Please observe the following rules - they are standard for all forums on the Internet. Don't post a new subject on an existing thread. This is called "hijacking" the thread. If you have a new question, start a new thread...
  14. KrisBlueNZ

    RS232 & Crossing RX/TX Lines

    Yes, the MAX232 has two drivers and two receivers. Often the second transmitter and the second receiver are used for flow control signals (DSR/DTR, RTS/CTS etc) for the same device, but you can use them for two separate devices if each device only needs TXD and RXD.
  15. KrisBlueNZ

    Activate a relay when resistance is within a certain range

    OK, here's my suggested circuit. It's based around an LM393N dual comparator IC. This device contains two circuits that compare two voltages and produce an output signal according to which is greater. They are shown as triangles inside the IC outline. With VR1 set to about 60 kΩ the series...
  16. KrisBlueNZ

    Flickering light (LED) circuit

    Where is the dimmer in your diagram in post #1? What was the reason that you connected a 0.47 µF capacitor across each group of LEDs? Where did you get the idea from? What is the brand and model number of the dimmer? What is the brand and model number of the lamps? Are they all the same? Do...
  17. KrisBlueNZ

    Activate a relay when resistance is within a certain range

    OK. I'll assume you don't want to do anything with the other button and you're only interested in a resistance of 240 kΩ. I will use a reed relay for the output because they are small and cheap and don't require much power. I'll draw up a design soon.
  18. KrisBlueNZ

    Activate a relay when resistance is within a certain range

    So you have two buttons on your steering wheel and when you press one of them, a 240 kΩ resistance is connected across two wires in the centre console which currently aren't connected to anything. You want to detect that specific resistance (a range of, say, 230~250 kΩ) and activate a relay. The...
  19. KrisBlueNZ

    Activate a relay when resistance is within a certain range

    That's a good start. Are we talking about a real car or a game contoller? Is this resistance connected to anything else? What are the buttons for? What do you want to activate with the relay? What is the overall purpose of the project? Please don't tell me it's a secret.
  20. KrisBlueNZ

    Current bypass

    You need to use a TVS diode that conducts when forward-biased. These are called unidirectional TVS diodes. In that case it will clamp the signal to about -0.8V before the resistor. If you're using an SMP3V3 as you showed in post #26 (but without the 38 ohm resistor, which you didn't explain)...
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