Lasers - I need a circuit that will turn on a laser for about 20 seconds.

Thread Starter

aaceith

Joined Dec 3, 2021
21
Greetings friends,

I have a cool problem I'd like your help with (pun intended) - I have a fan that I want to be able to accurately point and I would like to add a laser module to it to do so. I want to be able to push a button to activate the pointing laser such that after about 20-30 seconds it goes off on its own. The module is a standard 3-5V 650nm variety. I do not want to use a relay for space reasons. I plan to use an old USB plug's innards to generate the power for the circuit and wire it in the fan housing using a 3D printed mount to keep the laser module in place. Is this a life-changing application of electronics? No. Will it give me a fun project through which I can learn more about circuits? I sure hope so.

Thanks for your help.

P.S. I do have quite an assortment of transistors, MOSFETs, resistors, capacitors, inductors, etc. to work with.
 

ZCochran98

Joined Jul 24, 2018
221
Take a look at the 555 timer IC - an old but very reliable and simple chip. If you set it up in monostable mode (most datasheets for the 555 have an example of this mode) with a long enough period, you could use the output of that to trigger the laser module. In monostable mode, it'll turn on for a certain amount of time, then turn off for another amount of time (both times you can control by choosing various resistor and capacitor values).
If your laser module is as simple as "send in a signal to turn it on/off," then a simple 555 will be all you need. If you have JUST the laser, then you'll need a laser driver (which is as simple as a MOSFET and a resistor.
Here's a good link for a 555 tutorial that gives the basics of how to use it and then how it can drive a lamp/motor/speaker.
 

Thread Starter

aaceith

Joined Dec 3, 2021
21
Take a look at the 555 timer IC - an old but very reliable and simple chip. If you set it up in monostable mode (most datasheets for the 555 have an example of this mode) with a long enough period, you could use the output of that to trigger the laser module. In monostable mode, it'll turn on for a certain amount of time, then turn off for another amount of time (both times you can control by choosing various resistor and capacitor values).
If your laser module is as simple as "send in a signal to turn it on/off," then a simple 555 will be all you need. If you have JUST the laser, then you'll need a laser driver (which is as simple as a MOSFET and a resistor.
Here's a good link for a 555 tutorial that gives the basics of how to use it and then how it can drive a lamp/motor/speaker.
The laser just requires power - the circuitry to drive it is in the module. Will check out the link you referenced. Thanks for your suggestion!
 

Thread Starter

aaceith

Joined Dec 3, 2021
21
A simple 555 timer and a Mosfet output to drive the laser will work, plenty ready made PCBs on eBay or make your own on veroboard.
Great minds think alike - the other respondent said the same thing. Will see what I can come up with. Thank you!
 

MisterBill2

Joined Jan 23, 2018
13,797
Given that the TS is adjusting the fan aim by hand, how about just a SPST normally open push switch in series with the laser, and mounted to the fan, along with the small laser package. That will allow switching on the fan as needed to adjust the position, and switching off when the aiming is completed. Simple and reliable and cheap and easy.
 

Thread Starter

aaceith

Joined Dec 3, 2021
21
Given that the TS is adjusting the fan aim by hand, how about just a SPST normally open push switch in series with the laser, and mounted to the fan, along with the small laser package. That will allow switching on the fan as needed to adjust the position, and switching off when the aiming is completed. Simple and reliable and cheap and easy.
The simplest solution is the best solution! I love it and it will free me up to do some of my other projects. Thanks for the sage advice.
 

DickCappels

Joined Aug 21, 2008
9,512
When my children were young they would play their transistor radio, the leave it while the battery ran down. Eventually I got my hands some some MOSFETs that could hand 50 or 100 ma and made a crude timer. It saves a lot of money on batteries.

It was an N-channel (Siliconix VN88AF) so the source connected to the negative battery terminal. The drain connected to the place the negative battery terminal connected on the printed circuit board.

An electrolytic capacitor with a large (possibley 10 Meg) resistor in parallel with it was connected between the gate and the source. A push button, which was mounted on the top of the radio connected the gate and its capacitor to the positive batter terminal whenever the button was pushed, turning on the radio.

The radio played until the gate capacitor discharged sufficiently.

Crude, but it worked.
 

Thread Starter

aaceith

Joined Dec 3, 2021
21
When my children were young they would play their transistor radio, the leave it while the battery ran down. Eventually I got my hands some some MOSFETs that could hand 50 or 100 ma and made a crude timer. It saves a lot of money on batteries.

It was an N-channel (Siliconix VN88AF) so the source connected to the negative battery terminal. The drain connected to the place the negative battery terminal connected on the printed circuit board.

An electrolytic capacitor with a large (possibley 10 Meg) resistor in parallel with it was connected between the gate and the source. A push button, which was mounted on the top of the radio connected the gate and its capacitor to the positive batter terminal whenever the button was pushed, turning on the radio.

The radio played until the gate capacitor discharged sufficiently.

Crude, but it worked.
That sounds like it's worth building just for the joy of it! Thanks for your suggestion.
 

Thread Starter

aaceith

Joined Dec 3, 2021
21
Given that the TS is adjusting the fan aim by hand, how about just a SPST normally open push switch in series with the laser, and mounted to the fan, along with the small laser package. That will allow switching on the fan as needed to adjust the position, and switching off when the aiming is completed. Simple and reliable and cheap and easy.
I just finished the installation of the circuit, which I was able to hide in the existing power box for the fan. I cut open an old 1A, 5V Apple USB power supply, like you used to get when you bought one of their extraordinarily expensive phones, so it would fit in the available space. I put the momentary on switch on the outer casing of the fan and 3D printed a holder for the laser module that sits smack dab in the middle of the fan in line with the axis of the spindle. Thanks again for simplifying my efforts.
 
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