Search results

  1. Ashtead

    Driving a HDD motor

    This looks like it would run a little 3-phase motor at variable speed, continually. Such motors are used in hard disks to turn the platters, it is basically a small AC motor meant to run continually, and not really a stepper motor. Like other AC motors, it may likely have a lower frequency limit...
  2. Ashtead

    DAC 0808

    The schematic shows a DAC-08, (Analog Devices) which National Semiconductor calls DAC-0800, and this one is similar to, but not quite identical with the DAC-0808, or MC1408/MC1508 that other manufacturerers may call it.  The DAC-08 is somewhat more flexible, in that it may be used in some...
  3. Ashtead

    Counter

    The 74193 is a 4-bit counter  so it can only count to 15. But you can cascade two of these by feeding the CARRY and BORROW outputs from the first unit into the COUNT UP and COUNT DOWN inputs of the second unit., and then make some kind of circuit that feeds clock-pulses to the first (least...
  4. Ashtead

    Controlling a Relay via an LED Circuit

    Rob, I have usually fed the output of my optocoupler circuits into some logic circuits, and used a simple resistor-transistor combination driven from some other part of the logic. I have typically used something like in the attached figure, where the transistor's base is left open, emitter is...
  5. Ashtead

    Controlling a Relay via an LED Circuit

    LDR means Light-Dependent Resistor. These are made with some material that changes conductivity when illuminated -- the typical Cadmium-Sulfide LDR will have less than 1 kOhm when in the light, and something like 1 MOhm when in the dark.  This variance in resistance can then be used to control a...
  6. Ashtead

    steam engine indicator

    Could it be possible to record the pressure and shaft positions as they change over time using the sound card in the PC? There are two channels readily available and the sample rate available there would seem to be sufficient. It might be that the rate of change of the pressure signal is too...
  7. Ashtead

    value and tolerance of a resister

    To me the 2k2 part looks like it should be 2200 ohms, (2.2 kilo-ohms) and the final m could suggest 20% . There evidently is a British standard that specifies this, as opposed to the usual color coding. I found something about that here: http://xtronics.com/kits/rcode.htm This way of...
  8. Ashtead

    7447, 7448 decoders

    Hi gogo, The 2003 and 2803 that I mentioned are the NPN transistor arrays, grounded emitters and open collectors, and which have some resistors connected to the base so that they will work with input voltages as high as 5V. I sometimes prefer to think of them as sets of high-current...
  9. Ashtead

    7447, 7448 decoders

    Hi Autir, With logical circuits, there are a number of standard specs that apply to most of the circuits. For TTL as we are dealing with here, an input senses a LOW level when the voltage is from 0 to 0.8 V, and a HIGH level when the voltage is from about 2 to 5 V. When an input is driven LOW...
  10. Ashtead

    Need help in using Darlington Pair IC ULN2003A

    Oops! Sorry for the mis-information, I was wrong about the pin numbers: The correct ones would be Pin 8 Ground (or common emitter) and Pin 9 where the diodes go, for the 16-pin 7-channel parts. Pins 9 and 10 would have been right for the 2803 with 18 pins and 8 drivers in it... I don't think...
  11. Ashtead

    LED amperage question

    An LED will only draw the current it needs to light up. Usually this is something around 5-10 mA, so if connected to a power supply able to deliver 1A, it will still leave most of that 1A for powering other loads. As for printer cables, the usual 25-pin D to 36-pin Centronics has 17 signal...
  12. Ashtead

    Need help in using Darlington Pair IC ULN2003A

    Perhaps I can help out, I have used 2203s and relays in a similar way and they worked well. The 4511 has its outputs active High (voltage level is close to the positive Vdd) when segments are turned on. Each one of the 7 transistors inside the 2003 work as an open-collector inverter, which...
Top