# laser receiver project, is there anyone who would help put together for fee please?

#### jarvouk

##### New Member
Hi there I have a relatively simple project to construct but have no experience myself, I don't think it would be that hard for someone who has had the time to educate themselves on the topic. I don't have a lot of free time to research it myself hence the fee attached.

I wanted to design a small circuit that triggers a solenoid when an IR laser is detected. Ideally I wanted several IR diodes grouped together (probably in parallel) to make a larger catchment area. I am guessing the solenoid could be a cheap 5v one as I only wanted it to instantaneously hit out and strike a small bell when activated and reset immediately.

The laser is a 5mw red laser like the pointers you get, I think the IR diode receivers would work but you would know a lot more about that than me.

If anyone is interested and thinks this is something they might be able to help with could you let me know please? I am in the UK.

Many thanks,

Si

#### rjenkinsgb

##### Well-Known Member
I'd suggest a modification to the concept.
A simple on-off detector would be sensitive to bright light or reflected sunlight as well as a laser pointer.

Using a modulated beam gets around that; the light source is switched on and off at a high frequency (or even using a code, like a remote control) and the IR sensor ignores random brightness variations unless they switch at the right frequency or are sending the correct code.

#### jarvouk

##### New Member
Thanks for replying! I'm not adding or taking away from the source which would be a 5mw pointer, I understand it would be far more beneficial and effective as you suggest however it would be impractical to redesign the laser housing for my project. If I was building everything from the ground up it sounds like an excellent suggestion though.

The IR receiver could be housed in a shielded casing and recessed to protect it from extremes of light. I feel that would give it a suitable level of functionality and keep the circuit tinkering at purely the receiver end.

Does that make sense?

#### DrG

##### Active Member
I don’t have an interest in providing the service and I don’t live in the UK, but I did want to comment.

I would imagine that the price and problems of having something custom designed and built for you can become substantial and quickly.

While you think it is relatively simple, you also readily admit that you don’t know much about building the device, but will defer to those that have spent the time to learn about such matters and have the requisite skills and equipment. There is nothing wrong with that model and it is used all the time in areas like automotive repair. The difference is you and the person already have a good idea of what the desired outcome should be, i.e., a car that runs like it did before it broke.

I would suggest that one way forward would be to offer up a better level of detail about the specifications of the device and its purpose.

For example, from your description, I get the impression that you want something like this:

If the device is an audible laser target system, then there are many commercial products available and if they fit your specifications, they are probably going to be a lot cheaper. Additionally, there are probably a lot of DIY plans and write-ups of folks have built their own.

Finally, if you had some particular reason why the commercial products were not good enough, one might be able to modify them – again for less than designing and building one.

The better you provide the details of the “what” and the “what for”, the better your chances of getting what you want.

#### jarvouk

##### New Member
Thanks for commenting DrG. Yes that's the idea of a target system like the Laserlyte.

Surprisingly though there are not many similar products in what is a relatively niche market I guess, the Laserlyte targets are very highly priced which is why I was looking to make my own. I think theirs range from $100-$300 and importing from the US would not be desirable.

I have seen plans for laser tripwires on a lot of forums and as my design is very similar I had hoped it would not be a substantial step up in skill to rig in a solenoid instead of a buzzer. I just lack the knowledge to know which resistor, power supply to use.

If you think it's asking too much and probably too expensive and you are speaking from experience then I should probably scrap the idea for now then.

#### DrG

##### Active Member
If you think it's asking too much and probably too expensive and you are speaking from experience then I should probably scrap the idea for now then.

#### jarvouk

##### New Member
Oh nice find! This is the kit I ordered:

I'm not sure if it's compatible or the right one but I'll definitely order that laser shield thing and try it cheers!

#### DrG

##### Active Member
Yeah, that is a common starter kit that includes lots of stuff to play with and, for that, I think it is a very good idea. You will get hooked in no time....or you will get frustrated, believe that you bricked the dang thing and toss it while cursing loudly.

_____

If you look at the game shield that I posted in #16, the provided link shows the schematic and some sample code for using the shield. You actually have to solder all the components to the provided board and that board plugs right into the UNO that is included in your kit.

You can see that the targets are simple resistor dividers with a fixed resistor on top and three CdS light-dependent resistors on the bottom (which form the target area). The voltage at the junction will change when hit by the laser pointer. The Arduino has several analog to digital converters that can read voltage and provide a number that represents the voltage. Each target is connected to one of the converters. Thus, when the digital value read indicates a hit, the program can operate the buzzer and LEDs and any thing else that you can program to happen. That may not make any sense to you now, but it will.

The code also shows how to calibrate the targets for ambient light. I am certain that they will not work well in very bright light because they would already be near their maximum response - although you could do something about that.

Again, it is a pretty simple board but, low-priced and very UNO friendly - I am tempted to get one....but then I would need to get a laser pointer "gun"...then I would want to build new targets that pop up and twirl and play different sounds effects when hit and play disparaging taunts when missed and so on and so forth...and I really don't have the time .

#### jarvouk

##### New Member
A quick question re this kit:

Would it be possible to hook up more than one ldr in parallel on that same circuit or would that mess things up?

I wanted around 7 to make a nice circular target. In my ignorance I thought so long as only 1 is hit then it would function the same.

#### rjenkinsgb

##### Well-Known Member
Yes, you can parallel several, but it will also need the sensitivity adjusting as each will be partly conducting due to ambient light.

If you want a low component count and very adjustable sensor, an LM311 comparator would be a good basis.

Connect a preset pot (eg. 10K) across power with the wiper to the negative input, then a resistor (1k?) from power to positive in and the LDRs from positive in to 0V.

The output will go low when the light level is high enough. You can connect a LED and resistor in series from collector output to power +, or a low current relay coil with a flywheel diode, to switch a high power device.
Connect the emitter output to 0V.

It should work well on a 12V supply.

A quick google search finds something nearly identical, though for lower voltage and lower light levels:

The LED resistor should be higher for 12V, eg. 680R to 1K, and the 33K feeding the LDR much lower as you only want it to switch with high intensity light.