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  1. audioguru2

    Keys finder circuit

    If your 12V battery cannot supply enough current then its voltage would drop far below 12V. Maybe N4 doesn't self-bias itself at half the supply voltage. If its self-bias voltage is 1.2V lower than half-supply, then it will have its input voltage too high from D1. Then its output voltage would...
  2. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    Hi H198848, The LM317 and LM338 work very well but only when used within their ratings: 1) They can't dissipate much heat, so they shut-down when they get too hot. 2) The LM338 is rated for an input voltage no higher than 35V, so having a 30V output is difficult. 3) They don't have adjustable...
  3. audioguru2

    Step-up PSU with TL499A

    Hi Kain, You decided to use tiny little SMD parts, so have fun trying to solder them! ;D You have the TL499A running close to its power limit so maybe a little SMD one overheats.
  4. audioguru2

    Keys finder circuit

    Hi Lapsap, Good, it works. ;D I tested a 30mm diameter piezo transducer just now from a cheap alarm clock. The piezo has a small resonant chamber in front of it with a 3mm hole for the sound. As a speaker, it is poor until about 4kHz when it whistles very loudly. As a microphone, it is also poor...
  5. audioguru2

    Step-up PSU with TL499A

    Hi Kain, I didn't check your pcb layout, but it sounds like your TL499A is busted. :(
  6. audioguru2

    telephone related question #4

    Hi Walid, The 2.4V on the schematic is proof that the mute pin is not high (about 4.3V) nor low (about 0V) normally when there is no key dialing. Maybe it is an open-drain P-channel Mosfet that conducts during dialing which shorts the mute pin and microphone to 4.3V, muting the microphone. ;D
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Ta, 1/2W zener diodes are available spec'd at different operating currents. The project originally used 4.7k for R4, that set the current through zener diode D8 at only 1.2mA. If you use a 1/2W zener diode spec'd at 40mA, it won't work very well. I use a 1N5231 1/2W 5.1V zener diode in series...
  8. audioguru2

    theory question!!!???

    Having more pistons makes a motor run smoothly. ;D ;D
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Ta, Welcome to our forum. ;D TI shipped your samples very quickly! ;D The original pcb is fine except you must mount the rectifier bridge and Q2 externally on their own heatsinks. You might have difficulty fitting the larger R1, R2, R7 and C1. C5 is only a supply bypass capacitor and its...
  10. audioguru2

    Electronic Stethoscope

    Sure, if there isn't any friction noises then your idea will allow this project to display heatbeat rate. Yes if you still need its audio output. The new R5 will connect to the exising pin 7 of U1b. Then U4 connects to its output. The U4 circuit will need to be changed so that its output doesn't...
  11. audioguru2

    Step-up PSU with TL499A

    Hi Kain, I think your TL499A is working normally, but you are using it near its limit. To get "about" 50mA out (maybe 60mA?) at 20V, the 5V input will draw an average of 200mA (or 240mA) plus more for its efficiency loss. TI's application note shows its efficiency of between 65% and 80% with...
  12. audioguru2

    TIL 306

    Hi Source, It is too bad that you didn't post your request in our Datasheet Request forum. I use a few sites to find datasheets. This is from one of them: http://www.datasheetarchive.com/semiconductors/download.php?Datasheet=2051883
  13. audioguru2

    Fail in 100W amp. diagram!!!

    Hi Jabber, Welcome to our forum. ;D I noticed the errors in the schematic too last year and posted a fix for them. I don't know why the schematic in the project wasn't corrected and why my post doesn't show with a site search.
  14. audioguru2

    How electronics works

    He, he. Thanks for the excellent explanation. ;D ;D
  15. audioguru2

    Infrared Activated Switch

    Hi, Why not just use a transistor as an inverter to drive the relay? Why not use only a transistor to replace the relay? You can capacitor-couple the signal to the monostable so it times-out if the beam remains blocked. A single power transistor can be fed from a 555 through a...
  16. audioguru2

    Electronic Stethoscope

    Hi Xoy, For my Electronic Stethoscope-2 project, people have said and my tests have shown that the LED flickers with some hearbeats. This will give too many pulses to your counter. Therefore the circuit needs an integrator (very low frequency low-pass filter) to feed the LED driver that feeds...
  17. audioguru2

    solder

    I use 63/37 "electronic" solder which is the alloy percentages that goes instantly from liquid to solid as it cools, without the "plastic" mode that makes cold solder joints. I call 60/40 solder, "plumber's solder". ;D ;D
  18. audioguru2

    3-colours LED Solar Lights

    Hi Tnk, Yeah, those button cells don't last very long when they are used to drive LEDs, like those little keyring LED flashlights. You can watch them dim as the battery runs down. I got a laser and ultra-bright LED pen for Fathers Day and its 3 little button cells don't show any sign of running...
  19. audioguru2

    Infrared Activated Switch

    Sorry, I missed this part. The circuit for making mains AC power from a battery is called an inverter. An ordinary audio amp isn't used because it operates linear, and therefore would get very hot since the current into the step-up transformer is very high. Most inverter circuits have a...
  20. audioguru2

    Infrared Activated Switch

    Hi, You have a very good IR receiver that should be used with a 555 transmitter. If you use only 50Hz for the modulating frequency then a receiver made with an LM567 would pick-up mains hum. Our IR Remote Control project has a CD4013 flip-flop used as a latch that maybe you could use...
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