555 timer circuit

Discussion in 'Electronic Design' started by John Winstead, May 13, 2005.

I'm trying to build a 555 or 556 timer circuit that creates a 5 second pulse
to activate a small reed relay every 5 or 6 minutes. Can anyone help me
with that. Thank You.
John

2. OBonesGuest

So you want it to work in astable mode with Tl = 5min and Th = 5s

It's not that hard, read the datasheets.

3. Graham OrmeGuest

You'll have trouble getting a 555 to run that slowly. You'd have to use
a very low charging current for the capacitor, and it may be less than
the capacitor's leakage current.

I'd use a 4060 ( http://www.fairchildsemi.com/ds/CD/CD4040BC.pdf ) to
produce a pulse every 5 or 6 minutes then use that to trigger a 5
second monostable. I seem to recollect that the 555 can be used as a
monostable and 5 seconds would be do-able.

4. Ken SmithGuest

If you can live with the nominal 5 seconds VS 5 minutes ratio being
fixed you don't even need the 555:

Q(N) ---/\/\/-----+------------- Reset
!
V
---
!
Q(N+A) -------------+-------------- Pulse

Q(N) needs to be such that it has a period of 10 seconds so that it will
be low for 5 seconds after Q(N+A) goes high.

From the reset, it will be 10 seconds times 2^A until Q(N+A) goes high.
It will then remian high for 5 seconds. If you make A 5, the full cycle
will take 325 seconds.

5. John FieldsGuest

---
A 555 (even a CMOS 555) is kind of iffy at 5 minutes, so you might

+---------+-----+------+
| Vcc | | | +V
[510K] | +-->[250k] [0.1µF] |
| [100K] | | HC4060 +-------+
| | +-------+------+------+ |K | O----->C
+-------|Rs Rtc Ctc | [1N4148] [COIL]- - -|
| | | | | O--> |
+--|MR Q7 Q13 | +-------+ |
| +------------+----+---+ | +---------->NO
| | | C
+---[1N4148>]---+ +--[510]--B 2N4401
| | E
+---[1N4148>]--------+ |
GND

Set the pot to 160K and the output pulse will be about 5 seconds long
with a time between pulses of about 5 minutes and 20 seconds.

6. Terry PinnellGuest

See my reply in sci.electronics.basics, pointing you to this solution:
http://www.terrypin.dial.pipex.com/Images/555Astable5s5m.gif

7. Ken SmithGuest

[...]
A slight change:
You don't need two diodes.