Re: 555 timer circuit

From: John Fields (jfields_at_austininstruments.com)
Date: 12/30/04 

Date: Thu, 30 Dec 2004 11:58:24 -0600

On Thu, 30 Dec 2004 17:15:51 +0100, Dominic-Luc Webb <dlwebb@canit.se>
wrote:

>
>On Wed, 29 Dec 2004, Brian Lyons wrote:
>
>> On 29 Dec 2004 03:22:31 -0800, burtonfamily@dodo.com.au wrote:
>>
>> >Hello,I made a simple astable 555 timer circuit the same as the one on
>> >the 555 web site,but im having trouble working out the values of the
>> >two resistors and the capacitor so it will turn on for 3 minuts and off
>> >for 5 minuts.Could someone please point me in the right direction as i
>> >found the data *** a bit confusing.thankyou in advance
>>
>>
>> Try the following values:
>>
>> R1 = 430K
>> R2 = 630K
>> C = 1000uf
>>
>> T1= about 300 sec
>> T2 = about 180 sec
>>
>> Total = about 8 mins (because of component tolerances, it is difficult
>> to obtain precisian with long durations)
>>
>> Use single transistor to invert logic levels for T1 & T2
>>
>> A good 555 tutorial may be found at
>>
>> http://www.uoguelph.ca/~antoon/gadgets/555/555.html
>
>
>Hmmmm,
>
>Maybe this, together with one or more Johnson counters (4017) so that a
>higher frequency cap can be used? Also, maybe still higher values of
>R1 and R2 could be used (4.3 and 6.3 MOhm) with a 100 uF cap? 

---
How would you propose to arrange for the 38% duty cycle with a 4017?
-- 
John Fields