Search results

Search Forums New Posts
  1. KrisBlueNZ

    12v timer for pump

    The Maplin module you linked to is a good design. Ten minutes is a long time for a 555-based oscillator but it can work if you use a good-quality timing capacitor. That's C3 and you need to increase it to about 1000 uF. Don't expose it to high temperatures; this will increase the leakage in the...
  2. KrisBlueNZ

    12v timer for pump

    U1 contains two timer circuits. The left hand circuit is used as an oscillator. Its frequency is controlled by VR1, R1, R2 and C1. With the values given, the period between output pulses is adjustable from 3.36 seconds (VR1 fully counter-clockwise) to 6.65 seconds (VR1 fully clockwise). This...
  3. KrisBlueNZ

    12v timer for pump

    Hey, that's a clever idea! Yes, ten minutes is a long time for a 555 oscillator. I tried to find low-leakage electrolytics. A couple of Japanese manufacturers - Rubycon and Nichicon, I think - have low-leakage series, but they weren't available through Digikey. At least, not 1000 uF. So I...
  4. KrisBlueNZ

    Another circuit to analyse (MALAXOR speed variator)

    There are two definite errors in your schematic: the cathode of D1 must connect to a voltage rail so the relay coil can be energised, and the right hand terminal of the triac must connect to something apart from the resistor-capacitor suppression network that's connected across it. You may find...
  5. KrisBlueNZ

    In need for a high current switch

    Yes. The two diodes with voltages marked beside them are zeners. 0.5W types should be suitable.
  6. KrisBlueNZ

    12v timer for pump

    Thanks :-)
  7. KrisBlueNZ

    12v timer for pump

    Hi Brad and welcome to the electronics point forums :-) You can do this with a 555-based oscillator driving a transistor or MOSFET. Have a look at the basic 555 oscillator. It's the first diagram on this page: http://www.electronics-tutorials.ws/waveforms/555_oscillator.html You would need...
  8. KrisBlueNZ

    Problem with a homemade ECG

    If the signal you see looks like the differential of the expected signal, the problem is series capacitance (high-pass filtering), not parallel capacitance. This will be the input coupling capacitance in the sound card. Sound cards are not designed to (and will not) record signals in the region...
  9. KrisBlueNZ

    Looking for low resistance Analog SPDT

    My first thought is that a MOSFET is what you want. These are available with very low ON-resistances - down to 1/1000th of an ohm! They need a DC bias on the gate to turn them on. Some MOSFETs (called "logic-level gate" types) can switch heavy currents with a gate bias voltage of 5V or less...
  10. KrisBlueNZ

    Converting PWM output into a voltage using low pass filter.

    You need to run the switching converter at a fairly high frequency (50 kHz or more is typical) otherwise the inductor will be too big. A normal microcontroller won't be able to generate a finely controlled pulse width at these high frequencies. Also, a microcontroller won't be able to detect...
  11. KrisBlueNZ

    Same component's difference ???? amp,res,cap,tran

    As Steve and Dave have explained, the gain of that circuit is very dependent on the gain of the transistor, which varies from component to component. You can reduce and stabilise the gain of the circuit by adding a resistor in series with C4. Start with a value of about one fiftieth of R4. If...
  12. KrisBlueNZ

    circuit modification

    I don't understand why a microcontroller would cause a problem with purchasing. I would suggest something like the Microchip PIC16F1503-I/P which is a 14-pin DIP device. Digikey (http://www.digikey.com) has these ex stock for USD 1.08 in single quantity, and less for larger quantities. Each...
  13. KrisBlueNZ

    dual 1.5 K antilog potentiometer

    Hi Jeff and welcome to the electronics point forums :-) You could get 2k log pots and operate them in reverse, i.e. fully clockwise is minimum gain. You would need to connect the wiper to the opposite end of the track. A 2k pot will give a higher maximum gain. You could connect a resistor...
  14. KrisBlueNZ

    circuit modification

    Thanks KJ6EAD :-) I appreciate your contributions too.
  15. KrisBlueNZ

    circuit modification

    Hi and welcome to the electronics point forums :-) I've had a look at your schematic and I have a few comments and questions. 1. Is this a complete schematic of the board? I ask this because there are four OR gates, which would normally be a single CD4071 IC, but three of the gates are in U1...
  16. KrisBlueNZ

    Simple circuit design help needed please?

    Hi Juan, I can design a circuit to generate the reset signal when the button is held down. That's pretty simple and I will do it at no charge. You just need to find an off-the-shelf counter that suits your requirements. It needs to have separate inputs for increment and reset. Please post a...
  17. KrisBlueNZ

    Alternatives to LDR for audio signal.

    makaze, I'm afraid I'm going to have to drop out of this project. I haven't been able to find, or design, a suitable control circuit for the variable-gain amplifiers. Smooth, constant-volume panning requires half-cycles of sinewave to control the gains of the amplifiers. Sinewaves can be...
  18. KrisBlueNZ

    MOSFET power dissipation definition?

    Yes. First you have to decide how much junction temperature rise is acceptable. Then you look at the data sheet for the case-to-ambient thermal resistance. This figure may be specified without any heatsinking; this is common for through-hole packages such as TO-92 where the component body just...
  19. KrisBlueNZ

    IC heating up!!

    OK. If only one gate (pins 3 and 4) of the 40106 is used, exactly as shown in your schematic, and the inputs of the others are all grounded and the outputs are not connected, and the power supply is a clean 12V, I can't see any reason why the 40106 would be getting warm.
  20. KrisBlueNZ

    Please help understand this circuit .

    You seem to be guessing. You'll probably fix it quicker if you're a bit more methodical. You haven't posted proper pictures yet. I would like to see the underside, with IC markings clearly visible, and a closeup of the daughter board, as well as top-side views from different angles. (Some...
Top