I'm a hobbyist trying to learn the basics of the 555 timer, and am working off of the 50% duty cycle circuit from the National Semiconductor data sheet for the 555 (PDF pg. 10 Fig. 14) and have successfully prototyped the circuit on a breadboard, but am having difficulty identifying why my soldered protoboard version isn't working properly. Here's what I've looked at:
Schematic from the datasheet:
Below is how I've laid out the components and soldered them to the protoboard (as part of a larger design which is why explicit V_cc and GND are omitted):
(Bold lines are soldered connections, arrows are wire based connections. Red for V_cc, Black for ground, blue for intermediate connection and gold for primary output.)
- Pins 1, 5 are connected to ground (I recognize that 5 should go to a capacitor to ground, but have omitted it here as it worked without it on the breadboard and space was limited)
- Pins 2, 6 are connected together and their junction is placed between R_A = 10 k Ohm and C = 100 uF.
- Pin 3 is outbound.
- Pin 4 and 8 are connected together and to R_A with a 5V regulated source.
- Pin 7 is connected to R_B = 2.2 k\Ohm which is in turn placed between R_A and C.
I've gone through and taken voltage measurements and from ground
- Pins 2 and 6 are 0.9V
- Pin 3 is 0V
- Pins 4, 8 are 5.01V
- Pin 7 is 0.01V
My first thought was that I damaged something during the soldering process, so I went through and verified that the resistors and capacitor were functioning. The 555 sits in a socket, and each of the socket connections is going through.
So the big question is, what did I screw up in translating from the datasheet to this design? And, in general, what tests can I conduct myself to identify how to solve "why isn't my protoboard working" kind of problems in the future?