Understanding Tinhorn's Timer

Tinhorn

Well-known member
Joined
Mar 13, 2001
Messages
3,516
Reaction score
0
John,

Using that resistor you referred to "trims" the internal workings of the 555 IC's so that the time delay is changed.  That's about all I remember from my old school days.

that A+ is an error, my handwriting is horrible and the "Editor" made a mistake reading it,  that should be B+ as in Batt (+)

Also, here is a schematic that I feel more comfortable using because I've used it for several years now.  Some people who built that old one have had some Stability problems I think.  You'llnotice c5 is not even used, it's not really necessary unless the circuit is in an Electronically noisey environment....



Tinhorn
 

Brian

Inactive
Joined
Jul 30, 2001
Messages
1,194
Reaction score
0
C5 adjusts the threshold voltage.  It can be left off and it will use its internal 2/3 VCC or you can adjust it to get it to where you want it to be. In case you want the timing until reset changed.
Multiplying the Resistor value times the Cap value gives you a good estimate on how long the timing will be.  Say 10 uF and 1M would be 10seconds.

Brian

C5 just adjusts the trigger level so you are limited to how long you can time.  You are supposed to adjust the RC network at pin 2 and 3 to adjust the timing.  In this case C2 and R1 for the 2 min one and C4 and R4 for the 10 second timing.  

(Edited by Brian at 9:18 am on Jan. 11, 2002)
 

Advertisement



Top Bottom