Simple beam break sensor

[The Master]

I dont want people to be able to see the beam but if i cant get IR working then that might be the only option.

Thanks for the links. Ill have a read through them

[The Master]

Im trying to get this 555 circuit working but nothing is happening. Ive been following a few different diagrams on the internet and none of them seem to work

I found this calculator on google. I entered 38.5KHz, 50% duty cycle and 0.001uF (1nF) capacitor. It said to use an 18.7K resistor for RB and 0K for RA. Ive been using a 15K resistor with a 5K variable resistor as another website said. It doesnt really matter if its at the right frequency for now though. the LED just wont light up at all (im using an LED for now so i can see it working).

Ive tried putting the output through a transistor. Ive tested the transistor by itself and it works fine.

My circuit currently looks like the one on that calculator site. Does anyone know what ive done wrong or what to check next?

[mackrackit]

http://www.uoguelph.ca/~antoon/gadgets/555/555.html
The above tells a lot about the 555. Try the metronome sample and step it up.

[The Master]

Ive had a read of that page and i tried the metronome example but its still not working. I didnt have a 250K variable resistor so i use a 220K normal resistor and i connected and LED to the output (and tried through a transistor).

Ive tried 4 different 555s now so im sure its not the chips that are at fault

[mackrackit]

Been awhile since I have played with a 555, but I seem to remember something about different types.

What are the numbers on you 555s?

[The Master]

I swapped to a different breadboard and its starting to look a little better. The metranome circuit worked. Ive put it back how i had it to start with and it seems to be oscillating but not properly.

The circuit ive been copying is the Infrared Emitter 555 Schematic.

The chips i have are NE555N. Aparently the ones that start with NE are good for driving LEDs etc directly

[mackrackit]

Mold...Mold on the bread board.

You may be picking up some stray capacitance someplace.

[Archangel]

I don't want people to be able to see the beam, but if I cant get IR working then that might be the only option.

Thanks for the links. Ill have a read through them

red laser / infrared filter might work . . .

[The Master]

This seems to be working now. The calculators ive used say that RA (or R1) should be 0K. The circuit doesnt work unless i put a 1K resistor in. Ive tried a few lower values but the LED will go off after a set amount of time then not come back on. 1K doesnt give me a 50% duty cycle but it seems to be alright.

Once it was flashing correctly i changed the other values to what the calculator said and the LED came on but dimmer than usual so i assume its flashing really fast. I replaced with an IR LED and it now works over 2M

I hope it keeps working once its all soldered into a PCB :P