Search results

Search Forums New Posts
  1. KrisBlueNZ

    Tv ir receiver

    The demodulated remote control signal coming from the receiver is decoded separately by firmware in each board, which makes separate decisions about what the command represents and whether it is valid. Sometimes the firmware is not well written and it can misinterpret incoming commands depending...
  2. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    So you're saying that even with plenty voltage on SKT2, the circuit turns off when SW1 is returned to the AUTO position? That's not right. Re the reference voltage jumping around. Have you tried without the digital voltmeter connected? It sounds as if the voltmeter may be affecting the voltage...
  3. KrisBlueNZ

    Bottleneck 555's 0.2A Stuck project

    I'm afraid you will have to find that out for yourself. I understand the problem with Digikey. Their shipping charges to countries outside the U.S. are prohibitively high for hobbyists. I didn't know that you were outside the U.S. because you didn't say so, and you didn't fill in the "Location"...
  4. KrisBlueNZ

    Bottleneck 555's 0.2A Stuck project

    The important MOSFET specification is Rds(on). This is the effective resistance between drain and source when the MOSFET is turned ON by positive gate voltage. It is usually specified at one or more values of Vgs (gate-source voltage). In your case the gate-source voltage will be somewhat less...
  5. KrisBlueNZ

    Help: Driving a 5 inches 7 segment display

    OK. So you want to duplicate that circuit (actually two circuits, and with six digits instead of four), using larger displays that contain several LED elements in series and need 12~15V across the segment. Right? You need another supply rail at a higher voltage, and you need level shifting...
  6. KrisBlueNZ

    Bottleneck 555's 0.2A Stuck project

    The 555 can source or sink up to 200 mA (for a standard NE555, LM555, MC1455 etc). 1. You need a pullup resistor, e.g. 1k, from pin 7 of the 555 to the positive supply rail (pin 8 of the 555). 2. Drive the MOSFET gate from pin 3 of the 555. 3. Connect the MOSFET source (which is internally...
  7. KrisBlueNZ

    Electric drawer

    You may want to check out this thread: https://www.electronicspoint.com/motor-control-diy-t249865.html It relates to a similar system to move an archery target forwards and backwards. The mechanical details are different but the limit switch idea is there. We mainly discussed DC motors, not...
  8. KrisBlueNZ

    Hi-Fi speaker volume control question

    As Dave said, the problem is power dissipation. Any power that is not sent to the speakers must be dissipated somewhere, and that place is the series resistors. If you're not changing the settings often or quickly, you could do something with an array of relays, like a discrete DAC built with...
  9. KrisBlueNZ

    Help: Driving a 5 inches 7 segment display

    We need a lot more information. How are the displays multiplexed? Are you sure they're multiplexed? Post a schematic of what you have so far. Why are you using LSTTL? What year is it in your world? ;-) In general, if you're using common anode displays and multiplexing them, you just need a...
  10. KrisBlueNZ

    Bottleneck 555's 0.2A Stuck project

    http://www.digikey.com/product-detail/en/AOI516/785-1568-5-ND/3152480 30V, 50A, 9 milliohms at Vgs=4.5V, USD 0.55 @1-up http://www.digikey.com/product-detail/en/IPS075N03L%20G/IPS075N03L%20G-ND/2081218 30V, 50A, 11.4 milliohms at Vgs=4.5V, USD 0.73 @1-up The first one is in a through-hole...
  11. KrisBlueNZ

    Tv ir receiver

    The type of device Dave is talking about is an IR receiver module, which includes the photodiode, carrier filter, and demodulator, and produces a digital signal that pulls low when carrier is received. These modules are made by many companies and are universally used in TV sets and other...
  12. KrisBlueNZ

    Testing High Voltage Rectifiers

    If the rated forward voltage is 1.5V as you say, it may read open circuit in both directions on your multimeter, depending on how much voltage the meter applies. A better test would be a 9V battery, an LED and a series resistor e.g. 3k3. Connect like this: negative_probe ----------...
  13. KrisBlueNZ

    Op amplifier

    The electrolytic is in series with the resistor that forms the bottom of the voltage divider that is the feedback loop. It is there to provide low-frequency rolloff to the amplifier's response. The basic stage gain is about 15.5. (Calculated from 1 + (68k / 4k7).) If there will be significant...
  14. KrisBlueNZ

    Need help diagnosing H-Bridge

    The components may be rated for 40V, but the circuit design won't necessarily work at 40V. Many component selection decisions, including resistor values for example, are made based on the supply voltage. Without a schematic, I can't say for sure that the circuit would need changes to work at a...
  15. KrisBlueNZ

    Trying to fix home subwoofer amplifier. Any help is appreciated.

    OK, thanks for the helpful answers. If you're ordering and replacing a bunch of parts, you may want to replace the other TL072s that may have been damaged along with U4. U1, U2, U3 and U5 are all connected to the same rails as U4 and could equally have been damaged. U8 and U9 are slightly...
  16. KrisBlueNZ

    Help Finalizing LED Boost converter

    I'll pass on that question. Can anyone else answer it?
  17. KrisBlueNZ

    Help Finalizing LED Boost converter

    The boost converter inductor value is chosen based on the minimum and maximum input voltages, output voltage, and output current. If you change the output current significantly, the converter may not be able to regulate with the chosen inductor value. This is why brightness control is done via...
  18. KrisBlueNZ

    Trying to fix home subwoofer amplifier. Any help is appreciated.

    Thanks for the updated images. The reworked area is starting to look a bit better now. Yes, C135 looks like it needs to be replaced. The joint nearby looks OK now, I think, but I think you should carefully inspect the whole board for dry joints. Run this Google images search to get an idea of...
  19. KrisBlueNZ

    Trying to fix home subwoofer amplifier. Any help is appreciated.

    Please respond to each of these points. 1. Can you confirm that on both the good amp and the faulty amp, the discolouration of the PCB around R78 is much worse than the discolouration around R76? This is interesting because it indicates that the positive rail of the low-voltage circuitry draws...
  20. KrisBlueNZ

    Battery powered Current sink with low voltage cutoff

    First, there are three unrelated issues with your latest schematic. 1. You seem to have accidentally changed D1 from a high-current diode (1N5404 etc) to a 1N914. D3 should be a 1N914 but D1 still needs to be a high-current diode. 2. This is a drafting issue. Back in the day of printed and...
View older results
Top