Using a 555 Timer chip as a 1kHz oscillator

If you bung "555 timer" into Google, you'll get a list of tutorial and application sites several times longer than your arm.

Your problem is not with the 555, but the 1.5V supply. The 'standard' LM555 needs at least 4.5V, but there are low voltage versions available (from e.g. zetex). Have you been told what particular version you have to use?

Idle thoughts , but it occurs to me that if you haven't been given a spec. for the 555 type, then:

1) Draw up a diagram with a 1.5V cell at one end, a boost converter (to get from 1.5V to about 5V) in the middle, and a 'standard' 555 oscillator circuit (get one from one of the sources in my previous post - there must be an ordinary oscillator in there somewhere, and all you have to do is work out the values of the R and C for the time constant (to get the right frequency)) at the other. A block diagram would probably do depending on who's doing the marking and what they're looking for - you'll need references and lots of description or diagrams. (This is where you've got to find out what the bits are actually doing. If you can get this together, you're well on you're way to becoming a fine engineer).

1A) (Synopsis of (1) above) Draw up a diagram with a 1.5V cell at one end, a boost converter in the middle, and a 'standard' 555 oscillator circuit at the other. Make sure you know enough about what's going on to be able to explain it to someone.

2) Claim the class prize, because (assuming that the original device specified was a standard LM555 (and no-one else has spotted the deliberate mistake)) your's will be the only solution with even a hope of working!

3) Forgive JohnDG, 'cos he's had a pint or two. After lubrication, he tends to get slippery.

Or ya could use just two transistors as the oscillator and buffer the output with a third transistor.

Good point - why do you need to use a 555? I'd assumed it was some kind of exercise. There are lots of ways to make 1kHz oscillators!

Do you need a sine, square or triangular/sawtooth output?

Must it be equally on as off (Mark/Space ratio), or should there be some difference. The standard configurations of 555 as a free running oscillator, do not give equal mark/space outputs.

I forget which exactly, but one is 1/3rd of the time, the other is 2/3rds of the time usually (from memory!!). There is a simple trick with an extra diode that gives a near 1:1 ratio if required....

Somebody else has pointed out the voltage problems already for you......

Andy,

From what I have read, it is possible to get close to a 50% duty cycle by proper choice of resistors and capacitor with a 555.

I have been playing with one recently. The tough thing is that resisters and capacitors usually have fairly wide tolerances. Some say there are slight differences in the 555s themselves. So, the theoretical equations get you close, but getting components to get an exact frequency is tough.

Tad

Thanks for all the help!! I had found a configuration that would create a 100kHz signal as I needed, but it could only work as low as 3V. I was curious as to whether I was missing something that would let me use a lower voltage level. I've changed my design to work at the 3V minimum this configuration suggests. I'm going to test it and see how it goes, from what I've read the 555's are quite robust and can take some abuse. We'll see how it goes.

I believe the capacitor between pins 1 and 5 filters out any noise you can get from your input. Since I'm supplying this with a DC source I don't think that will be too much of a problem, but better safe than sorry. I'll see how it works both ways.

Thanks again for the help, I should be testing this next Friday, I'll let you know how it goes.

Out of curiosity, can you please tell us what this project is for? Fun, school, or what?

Haha, sure! Sorry about that!

I'm designing an RF ID chip for my fourth year project. I'm on a team of 7 people and together we're building the tranceiver and tag. Originally the tag was supposed to be a passive device so it would use power sent by the tranceiver, rectify it, power some sort of id chip (which I decided to just use an oscillator) which would turn a transistor on and off so that the signal coming in would see different impedances. This causing the signal to be absorbed and reflected in different amounts allowing the receiver to distinguish 1's from 0's.

However, after going through the specs we need to follow and what we'll actually be able to build by ourselves, we've decided to make the tag an active device and just power it using a battery. We're testing commercial components first to see what sort of outcomes we should get, then we'll be building our own parts. I'm using the 555 for this part.

P.S. That was me in that last post, didn't realize I had signed out :)