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  1. KrisBlueNZ

    led and potentiometer questions

    I've made a couple of small improvements to the run timer circuit to minimise the energy dissipated in the switching MOSFET at switch-off. The linear region is now only a few microseconds, instead of a few hundred! Don't use the previous version; QS might lose its smoke.
  2. KrisBlueNZ

    led and potentiometer questions

    Here's my suggestion. The top diagram is the PWM driver for the LEDs. The LEDs are connected in pairs of two LEDs in series with a current limiting resistor, and these strings are connected in parallel, and driven by QL. Each current limiting resistor should be about 100 ohms, to get 20 mA...
  3. KrisBlueNZ

    Audio Modulator Noise

    Does this click happen once in every cycle of the sinewave generator? Does it always happen at a particular point in the cycle? If so, which part? Have you looked at the LED? Does it increase and decrease smoothly in brightness? Set the modulation oscillator to a very slow frequency and watch...
  4. KrisBlueNZ

    Component help

    If your micro isn't doing anything other than controlling the LED and monitoring a pushbutton, you should be able to do the PWM in software. Especially if you only have four different brightness levels. Using multiple MOSFETs and multiple resistors will waste a significant amount of power in...
  5. KrisBlueNZ

    led and potentiometer questions

    How long do you want it to run for? If it's only a few minutes, you can do that with another 555 connected as a monostable (google it). In fact you can use a 556, which is a 14-pin chip that has two 555s inside it. There are various ways to gate the LED-driving 555 on and off. But if you're...
  6. KrisBlueNZ

    Audio Modulator Noise

    As Dave says, we NEED to see a circuit diagram. If you have something there that you're experimenting with, we need the circuit diagram or "schematic diagram" of it, and the modifications you've been making to it. If you can't trace out the circuit of the existing pedal, you can at least draw...
  7. KrisBlueNZ

    Component help

    The NTD5867 looks like a nice device but be careful with the RDS(on). At VGS=4.5V its guaranteed maximum RDS(on) is 50 milliohms (compared to 8 milliohms for the NTD4906). So at, say, 8A drain current, it will dissipate 3.2W, which would require heatsinking (a large pad on the board would be...
  8. KrisBlueNZ

    led and potentiometer questions

    Using germanium diodes won't affect the maximum and minimum duty cycle. Also, germanium diodes have fairly low current ratings and could be damaged when the duty cycle potentiometer is at either end. You can widen the duty cycle range to maximum by disconnecting the diodes from pin 7 and...
  9. KrisBlueNZ

    Component help

    Search on Digikey, Mouser or Newark. I searched for a good cheap N-channel MOSFET recently and found the ON Semiconductor NTD4906N. It's very cheap and seems to be readily available. Basic specs are: VDS = 30V ID = 14A RDS = 8 milliohms max at VGS=4.5V ON Semi case 369 as SMT and THT (DPAK and...
  10. KrisBlueNZ

    Do Wah Diddy guitar peddle

    I haven't seen anything that looks like that before. Can you post some pictures of it from different angles?
  11. KrisBlueNZ

    Vizio 42" model #: M420NV - HDMI

    It's interesting that the ports on your new board failed in the order that you used them. This seems to imply a problem with the signal, or perhaps the cable. The inputs may be poorly protected against surges and spikes. So, what are you connecting to the HDMI ports? And has it always been the...
  12. KrisBlueNZ

    Bad transformer replacement

    I had a fault with a similar-looking CCFL transformer in an old Sanyo LCD TV. CCFL transformers are a known common point of failure. I got my replacement from lcdparts.net.
  13. KrisBlueNZ

    Mysterious diode identification help!

    OK that's good. I thought maybe one of the capacitors was shorted. You can't check their values without a capacitance meter. It's also possible that a capacitor is breaking down when the voltage across it reaches a certain point, but I would expect some visible or audible sign from the...
  14. KrisBlueNZ

    dimmer for parallel or series LEDs with timer

    The need for programming that I see is the need to keep track of the time of day and translate it to an intensity figure that corresponds to the average daylight intensity at that time of day. It doesn't need to be highly accurate, but I would expect it would need to ramp up during the morning...
  15. KrisBlueNZ

    dimmer for parallel or series LEDs with timer

    I tried to think of a way to design your 24-hour brightness controller (to simulate sunlight over each 24-hour period) without an MCU (microcontroller) but it is just not workable without some kind of programmability. Do you have any programming experience? The hardware requirements are not...
  16. KrisBlueNZ

    dimmer for parallel or series LEDs with timer

    It's not NECESSARY to change to a 12V supply for your LEDs but it will make things easier. You can connect your LEDs in series strings of three. Each string will have a total voltage drop of 10.5V and a current of 350 mA so with a 12V supply, each string will need a series resistor of 4.3...
  17. KrisBlueNZ

    Confusing waveform driving PC speaker.

    If you "understand about the time constant" then you should know the reason for the "spiky" waveform. The time constant of 0.1 uF and 8 ohms is 0.8 microseconds, and the period of your waveform is 56 microseconds. So the signal you see across the speaker will be one positive and one negative...
  18. KrisBlueNZ

    dimmer for parallel or series LEDs with timer

    I totally agree with Steve. Connecting LEDs in parallel is SOMETIMES workable but not likely in this situation. Small differences between the LEDs will mean that some LEDs draw more current than others; they will get hotter, and this will reduce their forward voltage, so they will get hotter...
  19. KrisBlueNZ

    dimmer for parallel or series LEDs with timer

    That's useful information. You need to explain what you want MUCH MORE CLEARLY than that. How do you want to start the timer? What do you want the LED to do when you've started the timer? You need to describe what you want CLEARLY and FULLY.
  20. KrisBlueNZ

    understanding an RC toy mainboard

    It might be worthwhile posting some photos of the board. Use plenty of illumination (outside on a sunny day out of direct sun is probably best) and get as close as you can without losing focus. Both sides could be helpful. As for the motor's current consumption, you can measure it if you...
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