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  1. KrisBlueNZ

    Making a bicolor LED blink red/green

    Hi Eddie and welcome to Electronics Point :-) Here's another option that will work (barely) from a single 3V battery and will run for a reasonable length of time. The blink rate is determined by the product of RT and CT. You can vary either one to change the blink rate. U1 is a CD40106B...
  2. KrisBlueNZ

    IPL Repair

    Hi there and welcome to Electronics Point :-) It would have saved me some time if you had told us what IPL was. It seems to be "Intense Pulsed Light", used for cosmetic and therapeutic skin treatments including hair removal. https://en.wikipedia.org/wiki/Intense_pulsed_light Can you start by...
  3. KrisBlueNZ

    Impedance measure circuit ?

    So you have a TLV1117-3.3 regulator with a 100 µF electrolytic capacitor across its output, and you want to measure the leakage resistance of that capacitor? So you measure the "resistance" from the +3.3V rail to 0V without the capacitor, then add the capacitor and measure again? Have you made...
  4. KrisBlueNZ

    Heathkit IP20 Power Supply

    So you're using a 10Ω resistor as your output load? So you can set the output voltage to 15V and when you connect the load resistor, it drops to below 3V? Can you make some DC voltage measurements inside the power supply please. Set the output to 15V and measure the voltage, then with the load...
  5. KrisBlueNZ

    Noob Question About Current From Voltage Regulators

    When you post in an international forum on the Internet, you're "not in Kansas any more", and to use another famous quote, "When in Rome, do as the Romans do". If you think your reason is a valid argument, well, be prepared to be misunderstood again in the future. No, you don't understand. We...
  6. KrisBlueNZ

    Disable Mute Button

    Some other ideas. Desolder and remove the actual pushbutton (a "tact switch", usually) from the board; Cut the track to one of the pushbutton's solder pads - as long as there's only one track going to the pad, and no more than two pads are connected, otherwise you might stop other buttons from...
  7. KrisBlueNZ

    Controlling fans with PIC µcontroller - Transistor current rating issue

    Hi Maximo and welcome to Electronics Point :-) Yes, you can connect two transistors together as a Darlington pair, but you will lose a bit of voltage that way. Here's the Darlington option. All voltages marked on the diagram are approximate. When RB7 is high, Q1 will have enough base...
  8. KrisBlueNZ

    Noob Question About Current From Voltage Regulators

    Good advice there from Hop as usual. But I should explain why he used "I = E / R" instead of "I = V / R" for Ohm's Law. E was the original letter used for voltage. It stands for EMF, "electromotive force". I learnt Ohm's Law as "I = E / R" too. But at some time around the 1970s or 1980s I...
  9. KrisBlueNZ

    A little help on how to switch transistors

    A simple way is to find the two lines on the specification table that are above and below your IC value and choose the lowest hFE, to be on the safe side. In your case, 14 mA is between 10 mA and 150 mA so you choose the lowest of 75 and 100, which is 75. You can also look at the hFE vs. IC...
  10. KrisBlueNZ

    Noob Question About Current From Voltage Regulators

    You mean you have a power source, a series resistor, and the load? The load will draw current, which will cause a voltage drop across the resistor according to Ohm's Law. The current will be the same at all points in the circuit, but because the resistor will drop some voltage, there will be...
  11. KrisBlueNZ

    Strange problem with transistors flipping current

    OK, that circuit is called an H-bridge. It's normally drawn like the letter H for clarity - see https://www.google.com/search?q=h-bridge&tbm=isch The circuit you have there won't work properly because the two transistors with their collectors connected to the +9V rail are connected in the...
  12. KrisBlueNZ

    Noob Question About Current From Voltage Regulators

    Current can't be "dropped" the way voltage can. Current is a flow. All the current that flows into a circuit also flows back out. With a linear regulator, the current coming in is equal to the load current plus a small amount of current that the regulator uses internally for its own operation...
  13. KrisBlueNZ

    Heathkit IP20 Power Supply

    Thanks Ian! I've uploaded it to elektrotanya. Its location there is http://elektrotanya.com/heathkit_ip-20_assembly_manual.pdf/download.html
  14. KrisBlueNZ

    Is this a ceramic capacitor and is it bad?

    BTW the "bubbly stuff" around the disc ceramic capacitor is just glue to keep the ferrite beads on the lead wires from moving around. That type of capacitor doesn't contain anything that can leak.
  15. KrisBlueNZ

    Impedance measure circuit ?

    I guess the obvious answers are to either supply a much higher current initially, to bring the capacitor voltage up to the measurement maximum voltage quickly, then switch to the final current to do the resistance measurement, or avoid using a resistance measurement circuit to measure a...
  16. KrisBlueNZ

    LDR with two LEDs

    OK, here's my suggestion for a circuit with minimal parts. It can be powered from any DC supply in the range 4.5~12V. It should work down to 3V but the LED will be pretty dim, even if you delete RL. An ON/OFF switch, SW1, is shown if you want one. U1 is a CD40106B hex inverter with Schmitt...
  17. KrisBlueNZ

    Can i Send gps (nmea) data down a AUX plug?

    Ah, so you have an audio channel that is being transmitted along with the video, and you want to send your NMEA data through that channel. You can't just connect the serial data to the audio input because data needs to be DC coupled and the audio channel will not do that. The normal way is to...
  18. KrisBlueNZ

    Heathkit IP20 Power Supply

    Hi John Sorry I haven't been following this thread lately. I got frustrated drawing up the design because some information is missing. And I just don't like it much! The limited output current could be caused by R23 in combination with the silicon output transistors. Try disconnecting one...
  19. KrisBlueNZ

    Impedance measure circuit ?

    Google op-amp current source schematic to find examples of current sources that can operate down into the µA range. You just need to use a high resistance for the current shunt. The reason you wouldn't use a voltage divider is that the voltage you measure would not be linearly proportional to...
  20. KrisBlueNZ

    Python programming course help

    No problem. Yes I agree that it's a pretty tidy way of doing it. The reason you can compare characters numerically and this equates to an alphabetic comparison is the character set. Computers represent everything internally as numbers, and that includes characters. The mapping of internal...
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