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Aaron Cake
Administrator
Canada
6718 Posts |
 Posted - Mar 12 2006 : 10:15:59 AM
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A 200uA meter is an ammeter. You probably want analog as it will make it much easier to read. They generally aren't rated for voltage but you are looking at a meter designed for under 30V.
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yugi
Apprentece
7 Posts |
Posted - Mar 21 2006 : 4:29:07 PM
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Hi,
My name is Hugo Garcia.
I知 a mechanical engineer student from Colombia.
First of all, thank you very much for taking the time to read message.
I知 very interested in building the wireless auto tachometer.
I have been trying to get the tachometer to work for quite some time, without any success.
As you know, the design has a three position switch that enables the use of three different calibrations. Every time that I connect the switch in a position that creates conductivity between the base of the second transistor and one of the trim pots, the current reading goes to zero and stays there even if I change the resistance value of the trim pot. Because of this, I haven稚 been able to calibrate the system and to get it to work.
Could you help me? What I知 I doing wrong? I知 I connecting the transistors wrong?
I would really appreciate if anyone could help me.
Thank you again for your time.
Hugo Garcia
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Mar 21 2006 : 4:52:53 PM
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My assumption would be that the transistor is connected wrong. I apologize for the quality of the schematic...The collector of the transistor faces up, the emitter faces down.
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yugi
Apprentece
7 Posts |
Posted - Mar 21 2006 : 6:08:42 PM
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Thank you very much for your reply.
I will do the corrections and see how it goes.
Could I bother you again if it still does not work?
Thank you very much.
Hugo.
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yugi
Apprentece
7 Posts |
Posted - Mar 22 2006 : 5:29:57 PM
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HELP!!!
Aaron, I tried reconnecting the transistors the way you told me to and it痴 still not working. I知 using Fairchild痴 semiconductor 2N3391A transistors.
I checked every other component and they are all working fine. To do the calibration part I知 using the power source of an old PC. Could that be the problem?
I ask because I tested the circuit on my car today and I got the same result, but with a higher static reading this time, even after I switch to one of the trim pots. The reading does not drop to cero like it happened to me during the calibration with the PC power source (Like in my first message on the forum). However, during the test with the car, when I change the value of the trim pots, the reading stays the same.
Do you know what could be happening?
Do you happen to know the polarization voltages that are needed during calibration or operation in the base and collector of both transistors?
I hope you can help me, because I really want to get this project to work.
Thank you very much for your time and your help.
Hugo
Edited by - yugi on Mar 22 2006 5:33:00 PM |
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Mar 23 2006 : 09:23:55 AM
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Computer power supplies output DC...Unless you are talking about something else? As it says in the instructions you need to use an AC transformer. The reason is the precise 60Hz signal provided by the power company.
If the meter is being pegged to a value set by the pots, then increase the value of R1 and see what happens.
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yugi
Apprentece
7 Posts |
Posted - Mar 27 2006 : 7:42:22 PM
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Dear Aaron
Thank you for your answer.
I am using the PC power supply instead of the car battery during the calibration. To generate the 60Hz I知 using the AC transformer. I was wondering if maybe the PC power supply is not capable of giving enough current for the circuit. Could that be the case?
About the transistors, I asked about the polarization voltages, because I think that they are not working correctly and that they are the source of the problem. A few weeks ago, I tried to build the circuit with different transistors (2N2222) because the 2N3391A are very difficult to find over here. The circuit worked, but it was not accurate. Every time I would use it, the reading would change. Now that I知 using the right transistors, nothing seems to work.
Is the analog current meter necessary? It痴 required to have an instrument with inertia to compensate for the pulses? I ask because I have been using a digital multimeter to do the measurement. Could that be why my current readings are always cero?
Thank you for everything and I知 very sorry to bother you so much.
Best regards.
Hugo
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Aaron Cake
Administrator
Canada
6718 Posts |
Posted - Mar 28 2006 : 09:11:16 AM
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The PC power supply will have enough current to drive this circuit. However make srue that the PC power supply is actually giving you 12V. Some of them will behave strangly when running unloaded.
As for the meter, an analog meter is much easier to read since it has built in hysteresis. In theory a digital meter SHOULD work but it wouldn't surprise me if it didn't since M1 is rated for MICRO amps.
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yugi
Apprentece
7 Posts |
Posted - Apr 03 2006 : 11:42:00 PM
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IT WORKED!!!
Thank you very much for everything
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Aaron Cake
Administrator
Canada
6718 Posts |
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yugi
Apprentece
7 Posts |
Posted - Apr 12 2006 : 9:04:01 PM
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First of all, sorry about the late response.
I知 sorry to admit, that the problem that I was having with the tachometer was just a resistor. I bought every component and trusted their value to be the one I asked for, without checking. It turns out, that for R3, they sold me resistors of 47 ohm instead of 47k. That was all. After I corrected this, the circuit worked perfectly.
UPS!!!!
Thank you again for everything
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roshljo
New Member
4 Posts |
Posted - Nov 24 2006 : 08:55:58 AM
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Hi,
I built the circuit using the following transistors (PN2222A): http://www.ortodoxism.ro/datasheets/fairchild/PN2222A.pdf
It calibrates OK and works well below 3000rpm. Above 3000rpm instead of increasing the microamps measured with the rise of the rpm, the ammeter starts to decrease the readings! It does not matter if I switched it to 4,6 or 8 cilinders, it just does not want to generate anything more than 300 microamps... It behaves this way when tested on the car as well as when calibrating the device using a larger trim pot and increasing the resistance above 25k with the idea to calibrate it for 1-cilinder engine.
I need to measure rpm as much as 5000-6000 on a 4-cilinder engine, so what do you think is the problem here? Is the limit of this circuit 300uA or I am doing something wrong? |
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layzee_me84
Apprentece
Malaysia
5 Posts |
Posted - Dec 10 2006 : 02:53:37 AM
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| hello..my name is elda..im a student and i am interested in this circuit but can you send me the function of each part in this circuit?because i have to make an automatic switch on headlight for my project and that includes when the car is on the motion to turn on the headlights. so i want to use the wireless tachometer as a switch for my circuit that is why i need the function of each parts in the circuits..thanks.. |
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roshljo
New Member
4 Posts |
Posted - Dec 11 2006 : 10:42:52 AM
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Elda, using this circuit as a switch to turn on the headlights is possible, but I think it is unnecessary complicated. There are much simpler ways to do that - for example you can build a simple circuit with a resistor and a zener diode, which will turn on a transistor when the voltage in the car raises above some value, let's say 13.2V. This of course will work only if the alternator and the voltage regulator work properly.
May be something like this: |
Edited by - roshljo on Dec 11 2006 10:44:37 AM |
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wireless tachometer diagram
