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Herman the German

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Posts posted by Herman the German

  1. 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.





  2. 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.


  3. 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.


  4. 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.



  5. 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.






  6. Hi,

    I do not recommend using a voltage divider to indicate a functioning electric fence.

    Normal resistors are designed for a maximum voltage of 300V. Using those for a voltage divider you have to take care not to exceed the maximum allowable voltage drop per resistor.

    If you are going to use neon lamps try get some rated 50V/2mA (normally built into switches of electronic kitchen appliances). 

    Wind 4 to 6 turns of insulated wire around the HV-line and connect both ends of the "transformer" to the neon lamp.

    You will probably not be able to see the neon lamp flash during day time, but at night it should not not be a problem over a distance of 8km - a distance you can see a cigarette end glowing.

    To increase intensity of the flash you could use reflectors as they are often used for LEDs.


  7. Hi KelvinIV,

    there is one known and reliable method to calculate for filament resistance for me:

    Measure the current flow with the lamp being supplied by its nominal voltage.

    Then use Ohm's law to determine the resistance.

    Filament type lamps have very low cold resistance which increases with heating.


  8. I just counted the number of LEDs in that piece of junk. There are 42 red LEDs (forming the heart) , 84 yellow LEDs (forming the frame) and 16 green LEDs (for the letters "I" and "U" (btw. wrong English: You starts with "Y"  ;) ).

    Considering that half of the 84 yellow LEDs are on at a time the total current flow in the circuit will be exactly 2A!!!.

    (Can you afford installing a nuclear power plant in your backyard just to tell your beloved one that you love her? Try out your charm before wasting electric energy! Mine has been overwhelming throughout my life so far.  ;) )

    The small transistors will be happy if the clock rate allows cooling phases between switching them on.  ;D (The current flow for the red and yellow LEDs is 840mA with standard 20mA LEDs!)

    A better and power preserving way would be to wire the LEDs for least power (current) consumption and multiplex well planned groups of LEDs to reduce current flow to max 200mA.

    Multiplexing at frequencies higher than 100Hz will appear as steady light for human eyes. (They're damn slow!)


  9. Hi vannic,

    I'd go one further step and check the leverage going into the gear box. There should be a distinctive (relatively) long way of the push/pull rod. Reed switches are a bit large to sense different gears. Using a Hall sensor (TLE4905) you can place them narrow enough to avoid false readings. Their magnetic sensitive area is just a few square millimeters (2sq mm) large.

    Mounting small magnets on the rod you won't have to bother with cables going to the bottom of the shift lever.


  10. A very interesting task, indeed.

    I'm missing an important point. How will the user determine the relative direction of an obstacle?

    Telling me he will by using the stick you might as well forget about it. Many blinds have used a stick (and a specially trained dog) - consequently there is no advantage to your intended design.

    To hero999,

    I had expected a more qualified reply concerning fire detection. Where do you suggest to put the "hot" sensor in relation to the environmental sensor? A parabolic "antenna" is a great idea, but works only in one direction.

    I'd dislike the idea to warn a blind of fire in front of him while the flames burn him up from the rear.

    To the OP: Do a bit more brainstorming and you'll come up with a two dimensional warning system at least.

    Concentrate on weight problems which might arise if the sensor array on the stick gets too heavy for the user.

    Regards to both of you


  11. Hi Albert,

    you might substitute the photo transistor with a normal NPN transistor. Apply base voltage which will simulate the light passing to the photo transistor pulling the collector low.

    Switching the base to ground will then simulate an obstructed view switching the collector high.

    The connected OR-gate will function normally.


  12. A lead acid battery will charge very slowly if charged to 13.8V.

    If it's charged to 14.5V and reduced to 13.8V when the current drops below a certain level, it will charge much quicker.

    OK! Partially agreed.  :D

    Subtract 0.1V for a final charge voltage of 14.4V to make it safe!  ;)

    Beyond 14.4V any lead-acid battery starts gasing (Hoffman's electrolytic gas production facility)  ???  ???

    H + O mixed make a beautiful firework if touched off by the spark of a switch.  ;D

  13. Hi Joulian,

    the problem would be an omnidirectional sensor. It must be rotating either mechanically or electronically like a radar antenna.

    That sensor system being carried by a person has yet to be invented.

    What is your personal problem?

    Are you afraid being alone in the dark?

    Do you have reason to believe that somebody intends to threaten your life?

    If you honestly answer any of my questions with YES you don't have an electronic problem, but one a good psychologist can solve (together with you).



  14. It depends on what type of battery you have. To charge batteries you need a constant current source, but the method of charge termination varies from chemistry to chemistry. Lead acid batteries charge with a constant current then need a float voltage top off. NiCads and NiMH need a change in voltage with time charge (or temperature). Lithiums need an extremely accurate charge termination (to 100mV accuracy).

    Look at the MAX712/713 datasheet from Maxim for NiMH and NiCads.

    Lead-acid-batteries are charged with constant voltage e.g. 13.8V. Their charging current decreases while they approach full charging voltage.

    NiCads are charged with constant current.
  15. Hi Simon,

    I don't know the reason why some of my posts were deleted. I guess it's a simple data base error, since none the posts was abusing or aggressive. I did the design using Eagle (not 123 PCB). You might download a free version (Eagle light) from http://www.cadsoft.de.

    Eagle light is limited to a max. board size of 100X80mm and two layers (full professional version:800X800mm and 16 layers)

    You might want to play with the layout to make fit your needs. The board size is well within limits.

    Just don't care for the voltage rating of multilayer capacitors. They are rated starting at 63V and step up to 2.5KV. Using a 63V (small footprint of 1/10") types you will always be within limits applying those for low voltage circuits.

    You should take care of the appropriate voltage rating of electrolytic caps, starting at 10V up to 385V. For a supply voltage of 12V use caps rated 16 or 25V.

    Hi allvol,

    nobody is perfect.  ;D

    I assume you know about capacitances well, the mixup was probably caused by a power fluctuation in the brains.  ;)

    However, you just should make sure to post correct statements here. A newcomer might take a wrong statement for the truth and try to sell it as a "religion".  ;D

    Both of you, have a nice day.



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