Search results

Search Forums New Posts
  1. BobK

    rectifer issues

    Okay, now I understand. Just put the two AC sides of the bridge to the two end windings, and then take the + output of the bridge is your + and the center tap is the -. Leave the - output of the bridge unconnected! Then you have the same 2 diode circuit I suggested in my last post. Bob
  2. BobK

    rectifer issues

    I don't see your problem. If you want a single voltage that is the voltage of between either winding and the center tap, you can get the full rated current. You simply connect a diode with the anode to each end of windings with the cathodes tied togethen, and the center tap is your ground...
  3. BobK

    Learning remote circuit?

    If it was a matter of soldering an LED and a chip together and voila, it works, then you would be right. But I don't think that is the case. I doubt that there is a "learning remote" IC that works this way. As already stated, a learning remote would almost certainly use a microcontroller with...
  4. BobK

    DC-DC step-up help?

    Linear technologies has multiple step-up converters that would handle your project. Here is an example of one. http://www.linear.com/product/LT1370 Go to their site and there a form you can fill out to search for all compatible chips. But I see two problems with your approach: 1...
  5. BobK

    Possible to up Amperage of a 12V 500mA wall wart?

    http://www.amazon.com/Wagan-Amp-12V-Power-Adapter/dp/B000P7O5DG $14.95. You could not build one for less than this. Bob
  6. BobK

    Getting PCBs made

    I have used ExpressPCB and was very pleased. They have their own layout software which was very easy to use, or you can use other software if you choose. You can get 3 boards for as litte as $51 and they are top quality. I opted for solder mask and silk screen and 3 boards cost $75. My board...
  7. BobK

    Headphone amp circuit

    The LM4861 from National looks really nice. 1W into 8 Ohm. 2-5.5 V supply. Direct connection of speaker and unity gain stable. I just ordered a few of them myself. Only difficulty is it is SOP package, if you need a DIP you are out of luck. You can get SOP to DIP adaptors though. Bob
  8. BobK

    Where you guys usually to buy electron tube?

    Seeing as no one has supplied useful information... The last time I bought a vacuum tube, it was to fix my Hi-Fi so I could listen to my latest to the latest Beatles album (Sgt. Pepper) Bob
  9. BobK

    my daughter's science project

    Except that the transmitter and receiver in the link provided above are for data transmission and would require a microcontroller on either side. They would not be usable as is to do a simple on / off switch. The RC car solution is the best bet. You should be able to get a cheap one for...
  10. BobK

    Headphone amp circuit

    There are many headphone amplifier ICs out there. Go to a major supplier like digikey or mouser (in US) and search for them. Bob
  11. BobK

    How to make an electronic spark with low voltage?

    You don't really need a spark, just a small wire that will heat up enough to ignite the powder when power is applied. Bob
  12. BobK

    wien bridge circuit using buffer

    No, it has to do with buffering the load so that the load does not affect the oscillator stage. Amplitude stabilization is typically done with either a light bulb used as a negative temparature coefficient resistor or a jfet. Bob
  13. BobK

    Noob / peer circuit review - LED Power Source

    If I understand you, you are using a buck/boost converter to get 25.7 V and then running that through a linear regulator to get 9V to run the LEDs? That makes no sense at all. The idea of a DC/DC converter is to avoid the losses of a linear regulator, and you are basiclaly gauarnteeing a loss...
  14. BobK

    Stepper motor rated voltage vs max voltage

    I am not an expert on this, but I think what they mean by the max voltage and current is what you would apply to hold the motor in position. If you are actually spinning the motor, the applied voltage would be much higher because of inductance and back EMF. A stepper is not run by applying...
  15. BobK

    which differential amplifier can i use to amplify a low voltage input

    There are ICs specifally designed to do this, measure current across a shunt on the high-side: http://www.ti.com/corp/docs/landing/google/shunt05/?DCMP=A_Signal%20Chain_Precision_Amps%20&%20Linear&247SEM Bob
  16. BobK

    Driving LEDs from var power source - Efficiency

    Okay, maybe I am wrong about the efficiency. I was just going by the fact that I get a lot more light out of a 3W LED run at 20ma then an LED that is supposed to run at 20ma. I know that the output does not scale up linearly with current, so maybe by the time you get to full output on the high...
  17. BobK

    5.5KV Neon Sign Transformer for Tesla Coil is being weird. Please help!

    If the "transformer" is small and light, it is probably actually a switching power supply. The arc most likely activates a current limit shutdown. Are you using the "transformer" to charge capaciitors? If so, maybe a little (more?) resistance between the power source and capacitors would do...
  18. BobK

    newbie question about cap swap, hope you can help

    Same capacitance, higher voltage. Make sure you pay attention to the polarity if it is a polarized capacitor. Bob
  19. BobK

    Product Development

    It can think of a way to do it, but it would not be cheap. Each transmitter and the reciever would need a GPS. The transmitters would contnually transmit their positions and the receiver would calculate the distance from it's position, and sound the alarm when any transmitter was out of range...
  20. BobK

    Replacing Rechargeable Battery Power

    Let me get this straight, the negative terminal of the battery sitcks out of the device and is not connected to anything? I don't see how this works unless the device is immersed in a conductive fluid. Bob
Top