I want figure component values for 20 second 9v Time Delay Switch curcuit powering a 500mW Laser

Thread Starter

billharpo

Joined Jul 25, 2021
2
I am new to this forum. I've been appreciating the things I've learned from All About Circuits site for a long time, thanks.
I need to push a button to activate a 500 mW laser module for 20 or 30 seconds. Lots of advice on how to do it for a single LED. But this is for a 500mW (or larger) 9V laser module with a 9V battery. I have a handful of transistors around, lots of resistors & switches & several capacitors. I been unable to find any answers so I asking here. I know little about electronics and I am dabbling in micro-controllers and automation gadgets. I have the engineering and prototyping done on this but just can't figure out how to wire the "ON" switch! And this gadget needs to be as tiny as practical (or it'd have a relay and an arduino nano in it). Any help would be appreciated.
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Papabravo

Joined Feb 24, 2006
16,772
You can do it with a single chip called a 555, configured as a monostable multivibrator, also known as a one-shot. After a trigger pulse which can be generated by a button press, an RC circuit will keep the output in the opposite of its resting state for a period of time determined by the R (resistor) and the C (capacitor). The 555 is offered in different semiconductor technologies so be aware of that and be sure to check the datasheet. Search online for a '555 configurator" application if math is not your strong suit.
20-30 seconds may or may not be possible depending on the range of values required
 

Thread Starter

billharpo

Joined Jul 25, 2021
2
Sounds interesting but... The 555 time delay circuits I looked at seemed more complicated with more components than the NPN transistor timer with a Cap, a switch and maybe a resistor or two. I'm revisiting the 555 thing to see if maybe I missed something. Thanks for the suggestion. Sure wish I'd have pursued electronics instead of drafting back in the 60's when I was in high school!
 

Tonyr1084

Joined Sep 24, 2015
6,241
wish I'd have pursued electronics instead of drafting back in the 60's when I was in high school!
70's for me. But it has served me well. Ended up having an argument with an engineer who had no degree and his engineering experience was approaching one year, as he was an inspector prior to his getting the engineering job. He had no idea how to draw a blueprint, let alone use CAD. He and I argued about lead clearance from the pad it was connected to. He insisted it had to be 0.080" from the pad before the radius. The drawing correctly showed the detail outside the printed component and the leader lines went to the part where the clearance was critical due to high voltages. He insisted that the leader lines ALSO represented the clearance of the bend before soldering to the pad. It was a stupid argument, but being that he was the "engineer" the company took his position. I can't begin to tell you how much unnecessary rework that generated.
 

Yaakov

Joined Jan 27, 2019
3,464
I am new to this forum. I've been appreciating the things I've learned from All About Circuits site for a long time, thanks.
I need to push a button to activate a 500 mW laser module for 20 or 30 seconds. Lots of advice on how to do it for a single LED. But this is for a 500mW (or larger) 9V laser module with a 9V battery. I have a handful of transistors around, lots of resistors & switches & several capacitors. I been unable to find any answers so I asking here. I know little about electronics and I am dabbling in micro-controllers and automation gadgets. I have the engineering and prototyping done on this but just can't figure out how to wire the "ON" switch! And this gadget needs to be as tiny as practical (or it'd have a relay and an arduino nano in it). Any help would be appreciated.
.
How much current does the “500mW” laser module draw? Is the 9V battery a PP3 (plain old rectangular 9V “transistor” battery?

I think you are going to get very little battery life from your setup, and the terminal voltage of the battery will drop rapidly.
 

ElectricSpidey

Joined Dec 2, 2017
1,794
The problem with a simple transistor and cap delay is, you don't get a "digital" turnoff when the delay ends, I don't know how important that is to you but by the time you get a sharp turnoff by adding other components you might as well just use the 555.
 
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