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  1. K

    POWER OFF ON with delay

    What are you switching on/off/on to restart your system?...120VAC? ken
  2. K

    lm 723 dual tracking Lab PSU

    If you are not stuck on the LM723 (I couldn't find any dual-tracking supplies with it), there are a lot of of other options. Google: dual tracking power supply circuit Ken
  3. K

    direct current stimulation

    Was used for many years successfully and safely.  The idea of iontophoresis it to generate sweat on the skin and then analysis it. The circuit was also timed, and with over-current shutdown. Ken
  4. K

    direct current stimulation

    This is a constant current source I used as part of an iontophoresis current source for our Peds Pulmonary Function Clinic...many years ago.  The 67.5V battery was replaced with a 6vdc to 60VDC isolated DC-DC converter. The 60V gave us a wide dynamic range to compensate for skin resistance. Ken
  5. K

    Darkroom timer V2.0A project question ????? (Solved)

    Flux , except in extremely high impedance circuits like pH meter inputs, should not cause a problem.  Years ago I read in an H-P service bulletin concerning field repairs to PCBs, that unless "all" flux can be removed (think in-factory process) it should be left in place. Ken
  6. K

    Water level detections system

    http://www.picaxeforum.co.uk/showthread.php?t=12266 Something I did a while ago.  I would put the uC circuit at the roof tank, and run the control line to the pump "down" to the pump switch circuit. Mine was a continuous sense program, but if you only need to sense periodically, once a...
  7. K

    Water level detections system

    A problem with that design is that you are passing a DC current through the common and lo electrodes most of the time.  This will causes electrolysis that will corrode the electrodes.  Designs that have constant submersion of electrodes need AC drive/sensing to minimize this. Ken
  8. K

    Project related to medical equipment

    ECG/BP simulator with programmable outputs for various rates and abnormalities. Ken
  9. K

    need to build soil moisturizer level detector...

    Windshield washer pumps won't work.  They have plastic motor bearings. They're meant to run for only a second or two at a time.  If you try to run them for much more than that the bearings will melt.  I tried several different ones.  Been there...done that...smelled the burnt nylon. :( Ken
  10. K

    need to build soil moisturizer level detector...

    Why 12V battery to inverter to 240VAC pump? The inverter stage will waste power.  Just use a 12V water pump directly from the battery. http://www.faludi.com/2006/11/02/moisture-sensor-circuit/ Since your sensor probes will always be in moist soil, this circuit will cause the electrodes to...
  11. K

    Battery low voltage cut-off problem

    You need to add hysteresis feedback.  This will require a higher voltage than 10.55 (you select) to switch the light back. http://www.intusoft.com/onsemipdfs/LM324-D.pdf Look at Figure 13 for the circuit and formulas. Ken
  12. K

    nid help about a counter circuit.. :D

    Google: 4017 traffic light Ken
  13. K

    Blinking Halloween Eyes?

    Or, two LEDs in series with one resistor. (5v-1.7V-1.7)/0.01A = ~160ohms I use ExpressPCB's free schematic capture program.  http://www.expresspcb.com/ There are others like Eagle and PCB123, but I just like the ease and versatility of this one. Ken
  14. K

    Blinking Halloween Eyes?

    The relay is SPDT (single-pole/double-throw) so it's just a matter of using the common and normally-closed contacts, rather than the common and normally-open contacts. :) Ken
  15. K

    Blinking Halloween Eyes?

    LEDs, even the ones from a 115VAC strings, are 1.7VDC to 3.4VDC, depending on color.  So you will need a low voltage power supply anyway.  Here is a timer that could work.  The long period is 2.5 to 60 seconds and short pulse is 0.5 to 5 seconds.  These can be changed to your time range by...
  16. K

    Blinking Halloween Eyes?

    Jake, You want to run pairs of LEDs off of 115VAC...or just the timer? Ken
  17. K

    Blinking Halloween Eyes?

    Google: Blinking Halloween Eyes Ken :)
  18. K

    Solenoid Valve. Fluid Control Application.

    Isolating the the digital power ground from the load power ground, is as you say, to keep the large load currents from traveling through digital ground traces. These currents can cause voltage drops along traces that the digital circuits misinterpret as signals.  If you arr not using isolation...
  19. K

    Solenoid Valve. Fluid Control Application.

    Or: 4. Microcontroller>Darlington>Valve 5. Microcontroller>MOSFET>Valve If you don't need to isolate the valve's power supply's ground form the microcontroller's power supply ground, then #3, #4. or #5 will be the cheapest and easiest. #3 and #4 will require a base resistor, #5...
  20. K

    Solenoid Valve. Fluid Control Application.

    The linked data sheet said the power draw is 6VA (6 watts).  But, I would go with what is marked on the the valve, 3watts. Yes, by proportioning I meant PWM driven to achieve a variable flow.  Some people want to do this with ordinary valves...and it doesn't work. The coil current on your...
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