please dont rip this site

The 555 Timer chip

Terry Allen Steen, EE says

f = 1.44/[C*(Ra+2Rb)]

where

  1. Ra is between Vcc (Pin #8) and Pin #7 (Discharge)
  2. Rb is between Pin #7 (Discharge) and Pin #6 (Threshold)
  3. C is between Pin #6 (Threshold) and Ground (Pin #1)

ensure Pin #4 (Reset) and #8 (Vcc) are tied together, and Pin 5 (Control) needs a filter cap if the circuit has noise problems.

ALWAYS A L W A Y S ALWAYS! Start with the cap. Set it by pulse width. Use this table:

Cap(uFd)    Pulse width(Seconds)
--------------------------------
10.0             90m -  1.2
 1.0              9m - 120m
 0.1            900u -  12m
 0.01            90u - 1.2m
 0.001            9u - 120u
--------------------------------

Select your cap, THEN select the resistors. If you want to make it easy, ASSuME the resistors are the same value, then you can use:

f = 0.48/R*C <==> R=0.48/f*C

If your resistor is abnormal in size, you have either chosen the wrong cap, or you are doing some kind of real odd freq.

Mark Willis says:

[The] original 555's which were sort of power hogs; Use a low-power CMOS version, and make sure you have that version's datasheet if you use one, if you go the 555 route. Also, [you] could drive a 555 at a higher frequency and divide it's frequency down by a proportional amount.

Electrolytics have huge temperature coefficients, using one for timing a 555, you want something like a Mylar or other low-variance cap. Those gre REALLY pricey IIRC by the time you reach 100uF, so use smaller C, larger R, and watch the construction, leakage on those pins 6 and 7 will change your timing.

Roman Black says:

I've been playing with 555s since 10 years old. You can also use a single inverter from a logic chip to replace a 555 in 95% of circuits. For a 14pin chip you can get 6 oscillators vs 2 in a 556.

{see: http://www.users.dircon.co.uk/~doctron/chuckles.htm look at the gated astable circuit}

Also:

See also:

Questions:


file: /Techref/logic/555s.htm, 4KB, , updated: 2011/5/3 06:43, local time: 2024/3/18 22:22,
TOP NEW HELP FIND: 
54.172.169.199:LOG IN

 ©2024 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?
Please DO link to this page! Digg it! / MAKE!

<A HREF="http://www.piclist.com/techref/logic/555s.htm"> The 555 timer chip</A>

After you find an appropriate page, you are invited to your to this massmind site! (posts will be visible only to you before review) Just type a nice message (short messages are blocked as spam) in the box and press the Post button. (HTML welcomed, but not the <A tag: Instead, use the link box to link to another page. A tutorial is available Members can login to post directly, become page editors, and be credited for their posts.


Link? Put it here: 
if you want a response, please enter your email address: 
Attn spammers: All posts are reviewed before being made visible to anyone other than the poster.
Did you find what you needed?

  PICList 2024 contributors:
o List host: MIT, Site host massmind.org, Top posters @none found
- Page Editors: James Newton, David Cary, and YOU!
* Roman Black of Black Robotics donates from sales of Linistep stepper controller kits.
* Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters.
* Monthly Subscribers: Gregg Rew. on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.
 

Welcome to www.piclist.com!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  .