streets97f Posted October 27, 2005 Report Share Posted October 27, 2005 I building a pulse generator in an attempt to mimic the speed sensor on my car. (The speed sensor just generate pulses based on the rate of the turning transmission axle.) Here is the circuit i'm using:http://www.electronics.50g.com/cpg.htmI hooked up a 9v batt. to it and it feels like the 2n2222 is getting hot. I'm worried that the car ECU might draw too much current for the transistors. Can anyone suggest higher current substitutes for the 2n2222 and 2n2907A trans.I'm really a novice and would appreciate and suggestions. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 27, 2005 Report Share Posted October 27, 2005 Hi Streets,Welcome to our forum. ;DThe 2N2222 shouldn't get hot in that circuit. It would if its collector and emitter wires were reversed. Look-up its datasheet's pic of it at www.datasheetarchives.com .Your car's ECU could be damaged if your circuit feeds too much voltage to it. The ECU might have a max input voltage rating of only 5V. Quote Link to comment Share on other sites More sharing options...
streets97f Posted October 28, 2005 Author Report Share Posted October 28, 2005 Well i noticed as i i adjust the variable resistor past a certain threshold the circuit just puts out a continual voltage (6.8v and up) and the 2n2222 and the 50 ohm resistor get hot, but when backed down, the pulsing resumes and all is fine. Yes the ECU wants 5v. My understanding is that the var. resistor is there to adjust the voltage. If i choose a 12v source, can i adjust it to 5v? Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 28, 2005 Report Share Posted October 28, 2005 There is no reason why this circuit won't work at 5V, I've used this sort of circuit down to 3V before. I would recommend using some easier to build and more predictable like a NE555 timer. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 28, 2005 Report Share Posted October 28, 2005 Well i noticed as i i adjust the variable resistor past a certain threshold the circuit just puts out a continual voltage (6.8v and up) and the 2n2222 and the 50 ohm resistor get hot, but when backed down, the pulsing resumes and all is fine.Then don't change the variable resistor as much. Don't you have the 1M resistor in series with the variable resistor? The ECU wants 5v. My understanding is that the var. resistor is there to adjust the voltage. If i choose a 12v source, can i adjust it to 5v?The variable resistor adjusts the time between pulses a little. If the resistance is too low then both transistors will be turned-on all the time and the 2N2222 and 50 ohms will get hot.The amplitude of the output pulse is about 1V to 2V less than the supply voltage, so when the car's alternator is charging the battery at 14.4V, the amplitude of the output pulses will be about 12.4V to 13.4V. That's why I warned you that the output voltage might be too high.You could adjust the amplitude of the output pulses to exactly 5V if the circuit was powered from an LM317 variable voltage regulator set so its output voltage is 6V to 7V.Hey Alun,Have you ever seen a diode used as a low-resistance resistor before? Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 28, 2005 Report Share Posted October 28, 2005 A diode as a resistor?I've never seen it and I wouldn't recommend it either.If you wanted you could just clamp the output with a 5V zener. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 28, 2005 Report Share Posted October 28, 2005 If you wanted you could just clamp the output with a 5V zener.And with the unlimited current you can kiss the little 2N2222 good-bye! ::) ;D Quote Link to comment Share on other sites More sharing options...
streets97f Posted October 29, 2005 Author Report Share Posted October 29, 2005 audioguru: Are you suggesting adding a voltage regulating circuit like this one: http://ourworld.compuserve.com/homepages/Bill_Bowden/page12.htmYes there is a 1M res. in series but i think i have a 20% ver. pot when i should of bought a 15% var. res. with a lot of turns.I really know very little about electronics (i'm a bio major) so, if you guys could explain the descusion over the zener diode it would help.also, Alun I couldn't find a simple pulse gen circuit with a NE555...maybe you could point me to a site.thanks all... you all are very responsive, unlike other forums Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 29, 2005 Report Share Posted October 29, 2005 Bill Bowden's voltage regulator circuit would have an adjustable output voltage if you use a 1k pot wired as a rheostat for R2. You aren't powering it from a transformer so replace the huge capacitor on its input with 100uF. Change the output capacitor to 10uF.A zener diode at the output of your pulse generator would cause a very high current in the 2N2222 transistor and I am afraid that it will fail.Be aware that a multimeter can't accurately measure the voltage of pulses, so an oscilloscope must be used. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted October 29, 2005 Report Share Posted October 29, 2005 And with the unlimited current you can kiss the little 2N2222 good-bye! ::) ;DI should've explained this one a bit more, connect 22ohms in series with the zener and 22ohms in parallel with it.For a 555 timer solution look here Quote Link to comment Share on other sites More sharing options...
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