Capacitors

[Fractals]

I'm making a small FM transmitter for my car, following these (http://www.volunteerlabrat.com/default.html?goto=fmtrans.html) instructions. I am taking as many parts as I can from old motherboards and any PCB I can find lying around. Do the capacitors need to have the exact Farads, or could it be slightly off? That page doesn't say anything about voltage, do they need to be rated for the same voltage, or does it not matter, as long as I give it less? This is the simplest DIY FM transmitter I could find, are there any easier ways?

Edit: I have made a few computers and know enough about hardware, but I know almost nothing about electronics. I am learning everything as I go.

[MunkeyQ]

In general and especially in tuned circuits, the capacitor needs to be as close as possible to the value. So yes, the exact value.

The exceptions are for stuff like smoothing capacitors in power supplies where the capacitance isn't as critical.

As long as the capacitor's rated voltage is over what you're going to be feeding them, it's fine.

I'm moving this to DIY as it's probably more appropriate there.

[Fractals]

In general and especially in tuned circuits, the capacitor needs to be as close as possible to the value. So yes, the exact value.

The exceptions are for stuff like smoothing capacitors in power supplies where the capacitance isn't as critical.

As long as the capacitor's rated voltage is over what you're going to be feeding them, it's fine.

I'm moving this to DIY as it's probably more appropriate there.

Thanks.

What kind of electronics would have a lot of capacitors rated between 1uf-10pf? Specifically, 0.1uf, 0.01uf, 0.33uf, and 10pf. I'm kind of tired of opening every electronic device that I have laying around and inspecting every capacitor.

[MunkeyQ]

What kind of electronics would have a lot of capacitors rated between 1uf-10pf? Specifically, 0.1uf, 0.01uf, 0.33uf, and 10pf. I'm kind of tired of opening every electronic device that I have laying around and inspecting every capacitor.
Try older things as newer stuff tends to have surface mount caps which you can't really use. TVs and small radios are a good start. Or go to Radio Shack as they won't cost much.

However, at those values you aren't looking for electrolytics that look like little cylinders. You'll be after ceramic or mylar film capacitors, which look like little discs or shiny square-ish beads respectively.

These have a different method of telling you the value though. Instead of just having "0.001uF" written on the side, they have a three digit code. The first two digits are the first part of the value and the last digit is the number of zeros you add on to the end. This gives you the value in picofarads which you can translate to microfarads.

For example, a capacitor with 332 on the side would be 3300 pF.

[Fractals]

Try older things as newer stuff tends to have surface mount caps which you can't really use. TVs and small radios are a good start. Or go to Radio Shack as they won't cost much.

However, at those values you aren't looking for electrolytics that look like little cylinders. You'll be after ceramic or mylar film capacitors, which look like little discs or shiny square-ish beads respectively.

These have a different method of telling you the value though. Instead of just having "0.001uF" written on the side, they have a three digit code. The first two digits are the first part of the value and the last digit is the number of zeros you add on to the end. This gives you the value in picofarads which you can translate to microfarads.

For example, a capacitor with 332 on the side would be 3300 pF.

Thanks again. I've been looking out for those thin ones, I read about them on a page about capacitors. I only found about 10 of the thin ones on the 3 motherboards and 3 other random PCBs. Weird, because I remember seeing a shit load on some stuff I took apart a while ago. I'm back home from college for the summer, and my parents threw away most of my electronics.:mad: I'll try radioshack if I can't find any.

Edit: I have a CRT that hasn't been plugged in in at least a month. Would that still be dangerous? Would it have smaller capacitors?

[Archetype]

If you're making a one-transistor transmitter (i'm assuming this cause you said it was the simplest you could find) then the inductor value will matter most, just stick any ceramic cap in there and tune the inductor to the correct resonant frequency by altering the number of windings.

A CRT will have loads of small value capacitors, as long as you avoid the big ones and the tube you'll be fine, the electrolytics can stay charged for a year.
I know this from experience. :(

[Spatula Tzar]

Older radios, VCRs, and answering machines contain tons of little through hole electrolytic capacitors. CRTs do as well, but be sure to discharge the tube and any large capacitors before working on it. Remember the one hand rule when doing this.

[Fractals]

I'm having trouble finding a couple capacitors, and I want to avoid spending money. How exact do they need to be? Would 0.1005uF be close enough to 0.1uF?

[HLC]

I'm sure 0.1005uF be close enough to 0.1uF.
I think most capacitors have like 10% - 20% tolerance.
So anything close could work.
There's some with higher (tighter) tolerances.
Because of the slop in components, it's common to have tuning pots in circuits to get the circuit working right. There are also variable capacitors available for tuning a circuit.