electrical question

this may be off topic but my question is if i were to take a circuit with 450 millivolts put in a capacitor then a resistor, would i get a return signal that was below 300 millivolts and that would oscillate.

any help is apreciated

thanks

The formula for that is t=RC. That is, t is the time constant, R is the resistance and C is the capacitance.

However, you cannot take passive components in a pure DC circuit and make them oscillate, you would need an active component. What you would end up with is a bandpass circuit if the capacitor and the resistor were in parallel. That bandpass would be the frequency that has the time constant as determined by the product of the resistor and the capacitor.

ok this is the circuit im working with. i have a circuit with a 450 mv supply between the high and low signal circuits. i have heard that if you install a resistor in the low signal circuit and you put in a capacitor between the high and the low circuit with the connection of the capacitor after the resistor (as in closest to the supply side) you will get a return signal of bellow 300 mv with an oscillating signal. is this correct or not.

any help is apreciated thanks

ok this is the circuit im working with. i have a circuit with a 450 mv supply between the high and low signal circuits.

All your saying is that the supply voltage is 450 mV. Is this an AC or DC supply? Also, you are mentioning a high and low signal circuit. Are you saying that the 450 mV is what supplies these circuits or is this the difference of potential between the high and low?



[/QUOTE]i have heard that if you install a resistor in the low signal circuit and you put in a capacitor between the high and the low circuit with the connection of the capacitor after the resistor (as in closest to the supply side) you will get a return signal of bellow 300 mv with an oscillating signal. is this correct or not. [/QUOTE]


What value resistor are you installing? Ohm's Law requires two variables to find the third. Again, what do you mean by "high" and "low" circuit?
You mention a return signal, return to where? Where are you getting the 300 mV value? Are you saying that the resistor needs to drop 150 mV?

We are back to what I stated before, In order for oscillation to occur in any circuit, there must be an active component (transistor or semiconductor device). There are many different types of oscillators and the only one that I can recall is a phase shift oscillator that utilizes RC components but a transistor is still required to provide the feedback necessary to sustain oscillations.

I will go out on a limb and think when you are talking about a "high" and "low" signal you already have an AC component here. If that is the case, then the RC network you are describing could produce a harmonic based upon the frequencies of the high and/or low source.

This isn't rocket science but in order to say yes or no, more data is required.

here is the circuit. post converter ho2s


the o2s operation is as follows:

The PCM supplies a voltage of about 450 mV between the Heated Oxygen Sensor (HO2S) high and low signal circuits. The HO2S varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.

now if i were to take a resistor and put it in the low signal circuit, then put a capacitor from the high signal to the low signal circuit with the connection at the low signal curcuit above the resistor (as in between the resistor and the pcm) would i get a signal that is around the 100 mv to 200 mv and would have a slight oscillation. that way the pcm thinks its a properly operating sensor.

now a normal operating post convertor o2s's reading is normally fixed around 120-180 mv. it also raises and lowers slightly. that way the pcm can tell the sensor is operating correctly.

i figured a 1 meg 1/4 w resistor would drop the voltage enough. i had heard from someone, but i dont remember who that i could use a 1mfd capacitor to cause a slight oscillation.

You are not looking to oscillate as much as sending the spike that occurs when the Ho2 changes. In putting the resistor in series with the PCM doesn't sound right for you would be dropping some voltage across it. If you have talked to someone who has done this, for it sounds like you have, my first impulse is to think that you would want the resistor and capacitor in series between the pre and post cat sensors.

Why are you trying to fake out the PCM?

both convertors are junk. they cant do the job anymore and i was just wondering if i could just make a "sensor" that would act like an o2s instead of having to replace the convertors. when i watch the readings on the scanner the post convertor sensor readings are almost exactly the same as the pre convertor sensors, so i know the convertors are bad. where i live there are no emission checks so i was hoping i wouldnt have to spend the money to replace them, maybe even get rid of them. havent decided which way to go yet but i want to get the check engine light off and keep it off.

thanks for the input

this may be off topic but my question is if i were to take a circuit with 450 millivolts put in a capacitor then a resistor, would i get a return signal that was below 300 millivolts and that would oscillate.

any help is apreciated

thanks
can you help me, my 2000 silverados headlights have quit. i have traced the problem back to the bright and dim sw. the problem is i dont know what color the main ground is for the head lights i have ground the low beam side as a tempory fix. can you help?

ok the main ground for the headlights is a plain black wire. it is terminal E13 at the main connector under the dash at the bottom of the steering column. the highbeam is purple and the low beam is yellow.
all the dimmer switch does is control the ground so what you are doing will work for now. actually what you are doing is the best way to get the low beam headlights to stay on with the high beams.
since the dimmer switch controls the ground circuits it only applys a ground to the position your in so when its on low beam the ground is at the low beam circuit and so on, so if you give the low beam a constant ground it will keep it on when the high beams are selected.

any other questions just ask

My check engine light came on so I went to Auto Zone to have them pull the code. The counter man doing the work said his computer he was using said I have low voltage on my O2 sensor that is past the converter on the passager side.

He cleared the code but it came back on three days latter. So I guess somethings not right. Its been real cold here and I was wondering what are my options. A replacement sensor runs about $90 at Auto Zone. But I thought there may actually be some other type of problem.

Any suggestions?