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  1. Kiwi Bruv

    Mosfet Latching

    I built the circuit out of bits and bobs so now I need to buy a new amp I might as well build it out of an LM324 quad. Will this allow me to have the pwm at 20kHz? Where do I look in the datasheet to show me this? Circuit I have in mind is at www.cpemma.co.uk/pwm_erg.html
  2. Kiwi Bruv

    Mosfet Latching

    OK, I'll change the op amp. The pnp is to make the 555 timing cap charge linearly instead of exponentially so it gives a sawtooth output.
  3. Kiwi Bruv

    Mosfet Latching

    Thnaks Audioguru, one more question if you please. I am finding that up to about 15kHz the full 0 to 100% duty cycle is covered by the full range of the 10K pot. As expected the 555 puts out 4 to 8V so the pot divider at the comparator is designed to duplicate that range. However at 25kHz the...
  4. Kiwi Bruv

    Mosfet Latching

    Found it, wired the mosfet and driver trans wrongly. Both working now though! Sorry for the bother.
  5. Kiwi Bruv

    Mosfet Latching

    Audio guru, I don't think I explained properly. When the circuit powers up the bulb comes on fully. The signal is oscillating at the gate at 50% duty cycle but the mosfet isn't switching. I can remove the drive trans completely (source gate res remains in place) and the load remains on. So I...
  6. Kiwi Bruv

    Mosfet Latching

    I have built a simple PWM drive with a 555 and an op amp. The op amp drives a trans which drives a mosfet. However the mosfet seems to be latching. The mosfet is conducting, with no gate signal present, a test bulb lights brightly. When I apply the PWM to the gate the bulb dims as it should...
  7. Kiwi Bruv

    Electric assist bike

    Thanks. I've done alot of reading over the last week and now have a much clearer understanding of DC motors. I know I don't need a micrprocessor for the project but it just makes it more flexible and interesting for me. I am going to start with a motor & on off switch, then a PWM control...
  8. Kiwi Bruv

    Electric assist bike

    Thanks Guru, the chain tension switch is a great idea. I am beginning to think an electic assist bike is just a name for an underpowered electric bike. If you think of the rider as 100W motor. When the other motor is driving at a set speed and the 100W motor kicks in and takes some of the load...
  9. Kiwi Bruv

    Electric assist bike

    Alun, I've been thinking about this and looked on the 4QD site for some explanations but I still don't understand how the voltage and current can be controlled seperately. PWM will control the motor speed by applying bursts of full voltage (and current). Current limiting seems to work by...
  10. Kiwi Bruv

    Electric assist bike

    Thanks Alun, Suprisingly the mechanical part is quite straight forward. There are a lot of scooter and bike parts available now. I have welded a cog in place of the 1st gear on the back wheel. The motro drives this cog and the rider has the other 12 gears to choose from. The motor then sits...
  11. Kiwi Bruv

    Electric assist bike

    Hi, I am building an electric assist bike and need some help with the concept as I don't know much about motors. It will be a 300W 24V DC motor, driven by PWM with a microcontroller helping. I want the level of assist to be dependant on the rider - not have it pre-set by setting the motor...
  12. Kiwi Bruv

    PWM

    OK, thankyou
  13. Kiwi Bruv

    PWM

    I am building an electric bike. I am going to build a PWM circuit using a 555 chip to generate the PWM signal and and MOSFET to switch the motor power supply. I will drive it using a variable resistor initially and later a Picaxe microcontroller so I can do some fancy stuff. My motor is 300W...
  14. Kiwi Bruv

    Buried wire detector

    Thanks. I'm now using an LF353 at 12V, just because I had it available. I have 13mV to 1300 mV op amp output. It also seems to work OK down to 9V. I doubled the transmitter power to 180mA and this made a big difference in stability. Output now starts at 9mV  at 200mm from the wire and goes up...
  15. Kiwi Bruv

    Buried wire detector

    Thanks guru. I see how the rectifier would work and I can use that as an input directly to my microcontroller. I have reduced the power supply voltage to 6v , but I can't get my multimeter to show a voltage change as the sensor approaches the wire - but the audio output says different? I've...
  16. Kiwi Bruv

    Buried wire detector

    Thanks. :) I put the multi core cable on tonight and wired it to give 8 turns, it makes another big difference. Audibly we are out to about 15cm from the wire now and when on the wire it's screaming. I want to complete this circuit functionality before optimising the signal and trying to...
  17. Kiwi Bruv

    Buried wire detector

    Many thanks for being so explicit and taking the time. I understand perfectly.
  18. Kiwi Bruv

    Buried wire detector

    Many thanks. :) The audio tone is much clearer now and even my ears can detect it at about 100mm from the wire. Just about to research the band pass thing. I don't know how to "tune" the pickup coil, how do I determine the capacitor I need? The coil is a 820 microH choke. I can't describe...
  19. Kiwi Bruv

    Buried wire detector

    Many thanks guys, more questions below and
  20. Kiwi Bruv

    Buried wire detector

    After 3 mnths of experimenting with my wire following robot project I've cracked the sensor. This is no small achievement for me. Now I need some more help. I have an astable 555 driving an approx 100hz signal into a wire with about 80 mA @ 12V. My inductor is picking this up, I've used this...
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