Dual timer 556

Wendy

Joined Mar 24, 2008
23,415
Reread post #55. Try it without the load, you should see the LEDs come on one and a time (and only one at a time).

What is the point of R49,C42, R43,C36? There is nothing like that in the schematic I drew. You don't need them. Get rid of them and tie the reset pins to Vcc.

R47 can be removed, it isn't doing anything.

Pin 11 should have a capacitor on it (it was in my schematic).

Get rid of R29, it wasn't in my schematic.

Look, I drew a working schematic. Try it as is before going your own ways. I assume you are breadboarding this. I know both 555 and circuits, please use it as drawn. I am positive mine will work, yours I'm not so sure of.



Use the top schematic. Eliminate the relays, R1,R2, and the driver transistors, and tie a simple LED/resistor to the output of each timer to see when it is on. Each LED will light, and when it turns off the next one will light. When you have this working then add the power components.
 
Last edited:

Thread Starter

mpcotuong

Joined Aug 26, 2010
170
Hi Bill,

I am using exact your first circuit but not working. The first stage work ok but the second stage of 555 had pin 3 stay high all the time and third stage of 556B do not thing. may be chip chip bad? Have you tested your circuit.

My orginal problem of my circuit that

1) When apply power to my circuit the third stage go hig and make motor moving

2) The Replay from third stage has sticked all the time to make motor moving longer than 10 second

Thanks,
Kevin
 

Wendy

Joined Mar 24, 2008
23,415
These are the same design, over and over again, all simple monostables same as is described in this article, 555 Monostable (complete with signal conditioner). If pin 2 of the second timer (which is a conventional 555) is low the output (pin 3) will stay high.

The point is each and every one of these circuits works in exactly the same way.

One a 555 you will see the following voltages.

Pin 1 - ground, pin 2 - Vcc, Pin 3 - low, pin 4 - Vcc, pin 5 - 2/3, pin 6 - ground (but slowly goes high when timing), pin 7 - same as pin 6, pin 8 - Vcc.

This circuit works, it is reliable. If if doesn't work there is either a bad component or a wiring error. As I have said they are all the same, look at this schematic. Each timer triggers the next (which is why I wanted you to use an LED per circuit), so the signal will ripple down the chain, one after the other, with only one LED on at a time.
 

Wendy

Joined Mar 24, 2008
23,415
OK, I redrew this circuit to get you to see what is what. It is the same schematic with all the distractions removed. I reused your part numbers where the part values were appropriate. R4 is 10KΩ.



If you can get this to work then I will add the relays and motor, and go from there.
 

Attachments

Thread Starter

mpcotuong

Joined Aug 26, 2010
170
Thanks, Bill your circuit work with LED but the problem of apply power the second and third stage are on without input. Can we fix this problem. I would like to apply the power no one on until give the the input from NPN?

Best regards,
Kevin
 

Thread Starter

mpcotuong

Joined Aug 26, 2010
170
Hi Bill,

When I turn on the power the second and third stage has LED light up, it mean automatic give output for both stages. This is a problem because it make the motor moving when turn on the circuit power. I need to fix this issue, once turn on the power no one give output nor LED light up until I give input to NPN of TP5.

Can we fix this problem? Please let me know.

Thanks,
Kevin
 

Wendy

Joined Mar 24, 2008
23,415
OK, this is only during power up? No other time? I think I understand what is happening, but need to be sure.
 

Wendy

Joined Mar 24, 2008
23,415
Looks like I'm going to have to breadboard it. I didn't think about power up conditions.

Check this circuit out...



It is from the library of circuits I have put in my albums. It is a delayed power on timer. Looks familiar, doesn't it. Basically the timer is triggered at the same time power is applied. I think the same thing is happening with your circuit, since the previous 555 circuit is grounded.

You had the right idea delaying the power up using the reset, but it was poorly implemented. You had way too much time on the RC constant. The reset pin on all the timers can be kept low until the power supply settles down, then all the timers brought on line.
 

Thread Starter

mpcotuong

Joined Aug 26, 2010
170
Hi Bill,

Can you breadboard on the circuit which you aksed me to try. You will see the second and third stage LED light up once you turn on power. You need to try at leat ten times on/off. Sometime you will not see it but it will happen within 10 times.

Thanks,
Kevin
 

Wendy

Joined Mar 24, 2008
23,415
OK, the initial work is done, and I was able to duplicate your problems in general. They are two fold.

1. You must have bypass capacitors next to the 555's. This is a given, something so basic that it is usually not mentioned. Something like 0.1µF right next to each chip, along with a 220µF capacitor on the power buss in the general vicinity.

2. I added a common 10KΩ as show to all reset pins. The capacitance of the protoboard was enough to keep the timers from triggering. I'd add a 0.1µF cap to make sure it is sufficient. I tried it both ways.



On my layout I used 555s only. Hope this gets you going.
 

Attachments

Last edited:

Thread Starter

mpcotuong

Joined Aug 26, 2010
170
Hi Bill,

I am appreciate for your time to help work on this circuit alot. It's working ok now.

Thanks, again for your time to help me.

Bes regards,
Kevin
 
Top