newbie 555 timer help

[planedoctor]

Thanks for the assistance in advance.

I have a project I would like to make.
3v powering some TLC555's

Power on triggers [a]5 sec delay(low), then 5 second run of small motor(high), then [c] high to third circuit till opened.

Independently I have been able to make each circuit work but combining them is my issue.

R1= 1MΩ
C1= 4.7uF
T=5 sec

I have TIP120 and TIP42 available for motor and [c] output.
I guess I might be having isolation issues.
I don't have and design software to include a drawing.
Attached is the basic Monostable design I used.

View attachment 67112

 

[audioguru]

A TLC555 has a low output current when its supply is only 3V. Its minimum output high current is less than only 0.5mA and is less when a 3V battery voltage runs down. Its minimum output low current is about 5mA when its supply is 3V.

A TIP120 darlington transistor has an output voltage loss of about 1.5V at low currents so it wastes half of the supply to the motor.

A TIP42 or any other little power transistor needs an input of 1/10th its output current to be a saturated switch. But since it is PNP then the TLC555 drives it from an output low which can be a minimum current of about 5mA so the transistor can have an output current of 50mA.

"Typical" output current graphs of a Cmos 555 are shown in Intersil's datasheet for their ICM7555.

 

[planedoctor]

Thanks for the info.

How would this be best achieved?

What I have is a "useless box" I want to modify with a timing circuit.

When the switch[a] is closed I want a 5 second delay then turn on a motor[a] (1.5-3v, .70mA max draw) for 5 seconds then supply power to arm motor which mechanically turns off switch[a] and opens circuit.

What I was trying to do was have one 555 trigger the other. By itself the circuit worked and timed 5 sec but using output from 1 to trigger on other did not.

View attachment 67149

 

[alec_t]

The second 555 needs a power-on reset. Try connecting its reset pin to +12V via ~10k and to ground via ~0.1uF. BTW the component values shown give a 0.5 sec delay, not a 5 sec delay.

 

[planedoctor]

Thanks, I will give the reset a try. The whole circuit is powered by a 3 volt battery.

 

[alec_t]

My bad. For +12V read +3V.