laser trip timer using arduino

Thread Starter

seifullaah73

Joined Dec 13, 2019
51
Hi

I have a project to build a laser trip timer using a 5v small laser and an LDR.

The laser requires 5v and I can only think of using a 9v battery as it is portable and am thinking of using an 7805, 9v to 5v regulator and connect it in the following manner. Do I replace the 1K resistor and the LED with the load or just the LED.


It will be used outside.
I hope this won't run into that problem described in one of these threads that the battery usually drops to 7.2v and the 78m05 performs poorly under 8v.
It won't be constantly on, only when I plan to use it. for about 10 mins then turn it off until I want to use it again in about 10 mins later and turn it on again.

The LDR will be connected to the arduino to detect the trip in the laser.

Do I need a driver for the laser and which one would you recommend.

Thanks
 

eetech00

Joined Jun 8, 2013
1,869
Hi

I have a project to build a laser trip timer using a 5v small laser and an LDR.

The laser requires 5v and I can only think of using a 9v battery as it is portable and am thinking of using an 7805, 9v to 5v regulator and connect it in the following manner. Do I replace the 1K resistor and the LED with the load or just the LED.


It will be used outside.
I hope this won't run into that problem described in one of these threads that the battery usually drops to 7.2v and the 78m05 performs poorly under 8v.
It won't be constantly on, only when I plan to use it. for about 10 mins then turn it off until I want to use it again in about 10 mins later and turn it on again.

The LDR will be connected to the arduino to detect the trip in the laser.

Do I need a driver for the laser and which one would you recommend.

Thanks
Hi

The 7805 input voltage needs to be about 2v above the output voltage to maintain regulation.
So...if the battery voltage drops to 7.2v, the 7805 may not regulate.

Why not design for a 9v supply so you don't need the regulator?

BTW-The regulator should be configured for constant current, not constant voltage.

eT
 
Last edited:

ericgibbs

Joined Jan 29, 2010
9,864
hi 73,
I have some of those laser diodes.
Use +5V directly to the laser diode, they have an inbuilt resistor.
So in your 5V regulator you do not need the 1k resistor.

I found that the diode did not last very long when used directly on 5V, if you find the same problem add a 47R in series with the diode.
E

BTW: what detector are you planning to use.?

Caution: laser beam light can damage your eyes in seconds.
 

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Thread Starter

seifullaah73

Joined Dec 13, 2019
51
hi 73,
I have some of those laser diodes.
Use +5V directly to the laser diode, they have an inbuilt resistor.
So in your 5V regulator you do not need the 1k resistor.

I found that the diode did not last very long when used directly on 5V, if you find the same problem add a 47R in series with the diode.
E

BTW: what detector are you planning to use.?

Caution: laser beam light can damage your eyes in seconds.
Oh OK. I might just add the 47 ohm resistor just in case. Are you referring to the diode which connects from the output to the input? So the circuit should be something like below?

circuit.jpg

I plan on using an LDR with a black cylinder around the LDR to protect the LDR from outside light. The LDR will be connected directly to the arduino analog input port.
 
Last edited:

Reloadron

Joined Jan 15, 2015
5,370
Would the circuit be the same as the one I posted but instead of the LM7805 its the AMS1117-5. Or do I connect it directly to the IC.
This is the data sheet for the AMS1117 which shows the pinout. The pinout is not the same but yes, the circuits would be the same. I would also do as suggested and put a 47 Ohm resistor in series with the LASER, I also played around with them and on 5 volts they have a short life. On the regulators pay attention to the package.

Since you mentioned using an Arduino unless distance precludes it you could use the 5 Vout on most Arduino boards to power the laser still using a 47 Ohm series resistor.

Ron
 

Thread Starter

seifullaah73

Joined Dec 13, 2019
51
This is the data sheet for the AMS1117 which shows the pinout. The pinout is not the same but yes, the circuits would be the same. I would also do as suggested and put a 47 Ohm resistor in series with the LASER, I also played around with them and on 5 volts they have a short life. On the regulators pay attention to the package.

Since you mentioned using an Arduino unless distance precludes it you could use the 5 Vout on most Arduino boards to power the laser still using a 47 Ohm series resistor.

Ron
I will be using it on a track and the laser will be on one side and the LDR will be on the other side with the arduino so I can't use cable to connect arduino output to laser.

I found this board, but don't know if it's wired correctly because I don't see the diode

If not then I will create my own regulator circuit using that circuit in my latest post by move the resistor from in series with the diode to in series with the laser.
 

Reloadron

Joined Jan 15, 2015
5,370
That board should do fine. Diode D1 in your circuit and similar circuits are there only as added circuit protection, normally a common 1N4001 is used. They are not required so don't always expect to see them.

Hey based on your application you may want to consider using one of these sensor modules, I bought like 5 or 10 on Amazon for under a buck each. Rather than using an analog in just use a digital in since your beam is either there or not. They work great with the LASER you linked to.

Ron
 

ericgibbs

Joined Jan 29, 2010
9,864
hi,
If your power supply has a voltage output of 5V and can supply a current of at least 100mA, it will suitable. [ remember it may require a 47R OR reduce the voltage to say ~4V.]
Which type of sensor detector are you using.?
E

Footnote:
I expect the College are approving this laser work and are supplying suitable eye protection and advice.?
 

Thread Starter

seifullaah73

Joined Dec 13, 2019
51
Hi

Forget that power supply, because it uses a LM7805.

But I am using an LDR sensor.
I will use the ammended diagram you suggested.

The lecturer is approving the laser work.
 

ericgibbs

Joined Jan 29, 2010
9,864
hi,
A hint.
An LDR is sensitive to ambient visible light, so some form of collimation [ tube] will be required to shield the LDR from the room lighting]

Also remember to protect others from direct eye exposure to the laser beam
E
 

Thread Starter

seifullaah73

Joined Dec 13, 2019
51
There is difficulty in getting a through hole AMS1117-5 component.
i'm starting to think of getting a dc-dc converter board which has the ams1117 board on it like i posted above. Just add a 47R resistor in series with the laser.



Description:
Input: 6V~12V DC (input voltage must not drop below 6V).
Output: 5.0V 800mA (load current must not exceed 800mA)
Can be directly soldered on to PCBs using the pre soldered pins.
PCB size: 2.5cm x 1.1cm
Comes with onboard power indicator LED (red).
 
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