Maker Pro
Maker Pro

Guranteed pulse/no pulse on 555 power-on

D

DBM

Jan 1, 1970
0
I was wondering what is the best way to guarantee the presence or
absence (depending on the application) of a one-shot pulse following
power-on of a 555.

It seems that for pulse presence the trigger pin is always grounded
through a capacitor. However, I had pulses missed on power-on. For
pulse absence, a pushbutton is placed on the trigger pin between the
cap and ground, but I had pulses occur on power-on.

So, what's the trick to GUARANTEE that pulses occur or don't on
power-on?

Thanks!
Doug
 
M

mike

Jan 1, 1970
0
DBM said:
I was wondering what is the best way to guarantee the presence or
absence (depending on the application) of a one-shot pulse following
power-on of a 555.

It seems that for pulse presence the trigger pin is always grounded
through a capacitor. However, I had pulses missed on power-on. For
pulse absence, a pushbutton is placed on the trigger pin between the
cap and ground, but I had pulses occur on power-on.

So, what's the trick to GUARANTEE that pulses occur or don't on
power-on?

Thanks!
Doug

Guarantee is a pretty tough specification.
You need to inhibit the circuit till after all the power on glitches
have settled. But then you have the same problem with the circuit
that does the inhibiting. Look into microprocessor POR chips.
mike

--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
4in/400Wout ham linear amp.
Honda CB-125S
400cc Dirt Bike 2003 miles $550
Police Scanner, Color LCD overhead projector
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
D

dB

Jan 1, 1970
0
[email protected] (DBM) wrote
I was wondering what is the best way to guarantee the presence or
absence (depending on the application) of a one-shot pulse following
power-on of a 555.
Thanks!
Doug



To briefly inhibit the chip at switch-on connect pin 4 (RESET) to the
supply via an R and connect a C from pin 4 to ground. The chip will
then be held in its reset state until the voltage across the C has
risen high enough to enable the chip.

The solution you alluded to in your question (placing a C from pin 2
to ground - and an R to the supply) ought to guarantee a pulse at
switch-on. If it hasn't worked for you I can only suggest that the RC
product should be increased.
 
Top