Herman the German

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About Herman the German

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  • Birthday 04/05/1942
  1. TTL Pull-down and flyback diodes for Coil-Relays

    I recommend to use varistors (VDRs) to eliminate EMF pulses. They are available for automotive applications starting at 15V. If your chips are the old fashioned TTL components they require a low value pullup/pulldown resistor of about 470Ohm to 1KOhm. HtG
  2. campfire simulating circuit

    Hi, here is a fun project I made some time ago. I called it twinkling stars. Using different color LEDs, like red, orange and blue you might use it to simulate a flickering camp fire. If you like my design I will pass the Eagle files for easy building. Timer2 inhibits count at irregular intervals which makes the LEDs light pseudo-randomly. Frequencies generated must not result in an integer number when dividing f1/f2. HtG
  3. Voice record/playback design help

    Hi nexus_2006, you might want to try this circuit. It is built around an ISD2532 (32seconds at 8KHz sampling frequency). If that one won't suffice you might select an ISD2564 (64seconds). The device can be controlled locally and via a microcontroller. All necessary connections are available at SV2. Remark: The mic connects via two pads. However if a mic with built in Fet-transistor is used polarity may be changed turning the mic 180degrees. If you are interested in the Eagle files leave your full name and email address in a PM. Regards HtG
  4. Measuring roller skate wheel rotation

    Hi Lon, I assume the roller skates are fixed to a test stand. Using a permanent magnet on one side of one wheel and a counter weight on the opposite side you won't have any unbalanced situation affecting bearing life time. Use a hall switch to sense magnet passage (magnet must face the sensor with it's south pole) you can count revolutions employing a simple counter circuit. Check out the TLE4905 for your purpose and decide if it fits your needs. HtG
  5. Hi stube40, the question is: Do you really need a programmable Hall sensor for your application? The most simple way is using 3 pin hall sensor the same way as you would use any input from a button or switch. Check out the TLE4905 if it fits your needs. The TLE4905 switches output to ground (L) if pulled up by a 10KOhm resistor as soon as the south pole of a magnet gets into the magnetic sensitive field. HtG
  6. Solenoid driver circuit

    Hi Novice1, the type of diode used depends largely on the solenoid. The more current the solenoid pulls the higher the EMF pulse. For solenoids in the order of a miniature relay a 1N4148 will suffice. For high power solenoids I recommend using Schottky diodes like SBxx. HtG
  7. LED driver, constant current question

    If your LED draws more current than the power supply can deliver one thing will happen for sure: The power supply will blow up if not fused. You can't expect to get 750mA out of a 300mA power supply. HtG
  8. newbie

    Hi cuaytech, welcome to the forum. We're glad to share our knowledge and experience with you. HtG
  9. Simple LED circuit wanted for welding simulation

    Hi darkman101, ัyou won't require a microprocessor or a noise generator to simulate a welding arc. Here is a circuit suggestion which fires the arc pseudo randomly by means of two timer ICs and a decimal counter. It's important to have frequencies different a way that frequency division never results in integer values, e.g. 360/180. One timer clocks the counter while the other one disables counting for some clock cycles, thus generating a longer "weld arc". I suggest to use two individual timer ICs since a dual timer might not work properly, depending on the manufacturer. Here is the circuit and a PCB layout. Regards HtG
  10. Hi LEECH666, here are some numbers which should help you decide about the trace width. All results are based on a 160mm long trace, copper weight 1oz (35
  11. Hi sakbd.2010, this circuit has been buried some 20 years ago. Where did you dig it out? There are easier and more effective circuits. Just google for them. HtG
  12. Electric Fence Indicator/Display.

    Hi rfranzk, all resistors are standard 1/4W. If you have the schematic loaded in Eagle you'll get info about every part. Use the "I" symbol (I=info) and click the part you want to know more about. If you click on C1 you'll get the info that it's an MKS-02 (made by WIMA). Caps are not critical in that application and you might use ceramic or polyester caps. Tantalum and electrolytic caps are polarized and not to be used for AC which will be present at the circuit input with the shape of a pulse. With a cheap DMM you won't be able to measure uV (0.1mV=100uV). You won't be able to measure that voltage even with a mid class DMM since it won't zero accurately. Even with an oscilloscope you won't see any trace change in the Y-axis since most of the scopes require at least 2mV input. Just amplify the signal and check the circuit output voltage. If it is not sufficient you might use 470K for R3 to obtain a total amplification of 1,849 (presently 1,104) If all the changes are not successful you might increase the number of turns of the "transformer". I haven't tested the circuit, but it should do well. Regards HtG
  13. Controlling current through relay coils with resistors.

    Hi Ken, sorry, I just intended to move Arun's post. I'm not experienced yet in moving single posts. HtG
  14. This topic has been moved to [Circuit/General Requests]. because of hijacking another thread. [iurl]http://www.electronics-lab.com/forum/index.php?topic=20960.0[/iurl]
  15. Electric Fence Indicator/Display.

    Hi rfranzk, here is a circuit with an ultrabright blue LED (KINGBRIGHT) Using an OSRAM LED reflector you should see the device flashing even at daylight. The PCB design is purely single sided. The amplifier has a total gain of up to 1,104 and should suffice to amplify any voltage picked up by the "transformer". It is dimensioned to amplify 0.1mV from the transformer. For the transformer use only cable with the appropriate voltage rating. If you are interested to obtain the Eagle files please PM me your email address. Regards HtG A500_Reflektor_.pdf