40khz IR Emitter for Tagger

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dabnis

New Member
Hey guys!

I'm trying to build a basic lasertag setup w/ tagger and receiver, operating in the 40khz range.

All of the 555 timer based circuits I checked out online specifically for 40khz IR emitters required a potentiometer, which I did not want to use due to tuning and added variation.

So I found an online calculator and played with the values until it displayed 40khz frequency. Here are the parts I wound up using:

capacitors: .1pf, .001pf
resistors: 12K, 12K (separate 10K + 1K + 1K, linked together for each) *
555 timer
TASL6100 Infrared LED
* also a current-limiting resistor between the LED and 555 output

This is operated by a push-button switch. All housed in a SCH. 40 PVC gun. As this is a prototype gun, I have the end set up to where I can swap out couplers and try different diameter (and focal length) lenses. The LED is held in a bezel, which is inside a rubber grommet, which fits very snugly into the barrel.

I have a section of pipe that is marked with the focal lengths of various lenses that I use to slide the LED unit back in the barel, until the line matches where the lens will be.

The target (which is velcro'd to the players hat) is based on the Vishay 40khz demod (receiver), capacitor, and resistor. Output goes to a piezzo buzzer now, but I'm planning to add a pager motor to the scenario for a bit of feedback when the player is hit.

The tagger and emitter work. I've tested it with lenses and currently get decent range (and expect more with different lenses and better focusing).

Here are the questions:

#1 - How do I limit the transmitter to, say, .5 or .25 second pulses? Currently it emits as long as the button is held down. I've looked into 555 monostable one-shot circuits, but they don't provide for specific frequency outputs.

#2 - I'd like to use perhaps a counter circuit attached to the receiver (plan to build several of these receivers and hook together in series... would be worn on a headband) to keep up with hits. After 5 hits or so, the gun wouldn't work (which requires some type of setup between the gun and sensors to disable the gun. Phone line/jack connections or 1/8" audio connections, I'm thinking... just don't know the circuitry side of it)

#3 - I removed the resistor in front of the LED to drive it a bit higher. I figure this is safe since I'm not holding the trigger down (and hopefully can find a solution to question #1), but want to know if it greatly decreases life expectancy of the LED.

This is VERY basic stuff, I know, but we aren't currenty going for the more advanced scoring, player names, game types, etc, etc. and want just a basic 5-hits-and-you're-out last man standing type deal. THEN I want to move into other stuff like perhaps PIC programming and maybe MilesTag circuitry.

Just getting my feet wet at the moment.

neophyl

New Member
You are definately doing things old school style
The way we used to build them was with a 555 set to produce around a 10hz output with a 25% on period. This was for a pulse duration period. This was then fed into a basic logic gate (4081 iirc) along with the hit frequency. That would give you a basic machine gun effect. You can then use another 555 in monostable mode to control your shot duration 555. By varying the monostable length you get different burst settings from 1 up.

One problem you will be having is that the vishay parts arent designed for constant duration signals and expect bursts of signal. One reason why even the really old lasertag stuff used not only a carrier (40khz, 57.6khz etc) but also a tone frequency for the hit signal. The old Worlds of Wonder standard used a 57.6khz carrier with a 1.8khz 'hit' tone with a 567 tone decoder in the sensor part of it.

With a very short 'shot' period you can drive the IR led at around 1A and get much better range. Couple that with a 50mm lens with a FL of around 150mm and the range can be quite significant depending on your receiver. Even against a TSOP detector you can get over 300 metres if the sun isnt too strong and more at night.

Nowdays everything is microcontroller based of course. Personally Id jump in with a microcontroller from the start as its a good learning project and the circuits are much simpler. Its much cheaper to experiment with a micro based system than a hardware based one. The parts count (and board sizes) of the old fashioned setups get crazy once you start adding on some of the other stuff.

Jim's Milestag design is very very good for new designs although I still have a soft spot for the old WOW stuff

dabnis

New Member
Thanks, neophyl!

You know what... i think you're right.

I'm checking out the MilesTag stuff now. The MicroMT version looks really simple to construct. Not to mention, so few parts - very affordable.

So I think I'd like to take the MicroMT route. I'm going to go ahead and order the kit w/ printed circuit board and parts (if I get proficient, I can just order directly from Mouser and build on stripboard or something to save a few bucks later on) As far as the cables and off-board parts (piezo, IR LEDs, muzzle LEDs, switches, etc.) I have most all of that.

Also planning to get a PIC-PG2 from here. Around $20 - not bad I have already downloaded WinPic from here The hex files for the programming are provided on the MilesTag site. ...just kinda making out a checklist. Does that sound about right? Have I left anything off that would keep me from completing this project? Thanks for helping steer me in the right direction. I really think it would be best to just dive in with the whole PIC programming thing, as that seems to be where it's at. Thanks again! dabnis New Member Interesting... I posted a reply to this a few days back and don't see it. I understand I'm still under moderation but maybe that one slipped by? EDIT: Maybe I'm not under moderation. Hrm... Anyhow, I said something along the lines of this: I've ordered the Olimex PG2 programmer from Dontronics (only$20+, not including shipping) as well as the PIC16F8... chips, and other components. Hopefully this goes well.

Also, how much current can you theoretically pump through these IR Leds if doing so in short pulses (to increase range)? ...and does that dramatically decrease their life expectancy?

How long do IR leds in laser tag applications typically last anyhow, on average, based on playing time of say, a rental company with heavy use.

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Nigel Goodwin

Super Moderator
Interesting... I posted a reply to this a few days back and don't see it. I understand I'm still under moderation but maybe that one slipped by?
Sorry, since the latest software update I'm no longer prompted that there are posts awaiting moderation - so sometimes I miss them.

jimmythefool

New Member
Hi Dabnis,

I use PWM from a PIC/FET to pulse IR Leds @ 100 -150mA (60% duty cycle) with no problems.. I use them for Beam Breaks,(which are on 24/7) along with a Vishay equivalent IR logic receiver. In my particular application, I have never had the problems mentioned above regarding the device not holding state with a constant pulse.Although I have heard of this, and I don't doubt the problem exists.. Might be worth speaking to a Manufacturer's tech guy regarding lifespan when over-driving the LED

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dabnis

New Member
No problem, Nigel. Thanks a bunch!

Good information, Jimmy! I think I'll try and get in touch with a Vishay tech guy on lifespan and over-driving.

Much appreciated!

neophyl

New Member
The TSAL leds we currently use are pulsed at around 1-1.5 amps. Of course the duty cycle once you factor in carrier/tone and pulse duration is only around 5-12% depending on rate of fire.

Ive had the same IR leds in my older kit for years (12+ on my oldest gun). Of course a commercial operation gets ALOT more use out of their gear so the lifespan is less. That being said replacement of ir leds in the equipment at BFS's main site in brisbane wasnt a common thing. Maintenance was more for physical damage to the guns/sensor units metalwork as customers are hard on it.

dabnis

New Member
Excellent info, Neophyl!

I had heard to mount the LEDs in a way that they can be swapped out easily (and that they should be considered a 'consumable'), but never really read about how long they last. They're cheap enough, I guess... but it's still good to know they should last a while!

dabnis

New Member
So...

I took the newly-arrived Olimex PIC-PG2 programmer, a blank PIC16F684, these instructions, hex file supplied here, and attempted to program the chip.

The light on the PIC-PG2 comes on, flashes when I hit erase, and otherwise gives me indications that everything is wired correctly. I've checked the pinout multiple times (even redid it on a protoboard the 2nd time to be sure) and followed the instructions closely, changing the software options exactly as recommended.

However, when it comes time to program, I get constant errors. I'm trying to get some help from LaserForums, but to no avail.

I've posted a question there asing if it could be the power supply (ie. my desktop may only be supplying +5v). This has been mentioned multiple times in other forums - that the programmer may not be getting enough juice from the serial port. Especially an issue with laptops but apparently happens on desktops too.

#1) I don't know which pin to check w/ multimiter to verify
#2) If it is only supplying +5V, how can I get the ~13v to it?

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dabnis

New Member
Going the "old-school" route, I've built a 40khz oscillator that is composed of the following:

A 555 timer in monostable/one-shot mode, to provide an approx. 1/4 sec pulse.

A 555 timer in astable mode (using a .01 uf cap, .001 uf cap, and two 12k resistors) to generate the 40khz. Output is connected to an IR LED.

The monostable's output is connected to the astable.

What happens is when I push the button and quickly release it, the astable emits for the given time and shuts off, sending a clean on-to-off pulse to the receiver circuit (which is just a 40khz TSOP demod, cap, and resistor with output going to a piezo buzzer). This should work fine for counting, since the signal is being debounced by nature of the monostable circuit.

The problem is that if the button is held, the signal continues to transmit. I would like for it to only send a 1/4 second pulse and stop regardless of how long the button is held.

Is this possible?

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ecerfoglio

New Member
Going the "old-school" route, I've built a 40khz oscillator that is composed of the following:

A 555 timer in monostable/one-shot mode, to provide an approx. 1/4 sec pulse.
A 555 timer in astable mode (using a .01 uf cap, .001 uf cap, and two 12k resistors) to generate the 40khz. Output is connected to an IR LED.

The monostable's output is connected to the astable.

What happens is when I push the button and quickly release it, the astable emits for the given time and shuts off, sending a clean on-to-off pulse to the receiver circuit (which is just a 40khz TSOP demod, cap, and resistor with output going to a piezo buzzer). This should work fine for counting, since the signal is being debounced by nature of the monostable circuit.

The problem is that if the button is held, the signal continues to transmit. I would like for it to only send a 1/4 second pulse and stop regardless of how long the button is held.

Is this possible?

That is a "classical" problem with the 555 monostable: while the trigger is held down it's output remains up.

The solution is rather simple: AC coupling of the trigger signal

Connect one side of your button to ground and the other side to a pull up resistor.

Connect a small capacitor between the 555's pin 2 (trigger) and the button-pull up resistor junction.

Add a second pull up resistor between pin 2 and +V

The values are not critical, you may use smething like 10KΩ for the button's pull up, 100KΩ for pin 2's pull up and a 10nF = .01F capacitor. This gives a time constant (=RC) of 10nF x 100KΩ = (10 x 10^-9) F x (100 x 10^3) Ω = 1 milisecond (lots of time to trigger the 555 but very short in human terms)

dabnis

New Member
I will give that a try! THANK YOU!!!!

dabnis

New Member
ecerfoglio: Would it be possible to use a higher value resistor (like 1M or 2.2M) and smaller capacitor? I don't have any 10nF/.01F on hand, but I do have several .01uF that I could use.

ecerfoglio

New Member
ecerfoglio: Would it be possible to use a higher value resistor (like 1M or 2.2M) and smaller capacitor? I don't have any 10nF/.01F on hand, but I do have several .01uF that I could use.
.01 Farad ... That´s a BIG capacitor. I intended to write 10nF = .01µF That is the value that you have.

Sorry for the typo.

dabnis

New Member

No problem! Glad to know I can use some existing parts.

Thanks again!

dabnis

New Member
That worked! I have the two 555 circuits connected and the emitter stops after a small pulse, even if the button is still pressed.

The first time I tried, I had the IR LED's + connected to the output of the 555 oscillator and the IR LED's - connected to ground. This gives a very weak pulse (I guess because it is now going through two 555s, whereas the strong pulse before was through a single 555 and less components.)

So I decided to try a 2N2222 transistor, connected like so:

E -> Ground
B -> Output pin 3 (from the second (or astable) 555 timer)
C -> IR LED -> 100k resistor -> +V

That provided a much stronger pulse, but I just want to be sure that is hooked up properly. ie. I'm wanting the IR LED to be pulsed at high currents, but not run at a high current continuously. Does that make sense? In this type of connection, it constantly has juice flowing to the anode/+. But... I guess it doesn't matter until it has ground applied (triggered via output pin 3 through transistor)

Eez dat right?

Thanks for all the help so far!

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dabnis

New Member
Do I have that 2N2222 hooked up properly? It behaves as expected, just want to be sure it isn't supposed to be inverted or something.

ecerfoglio

New Member
------------

So I decided to try a 2N2222 transistor, connected like so:

E -> Ground
B -> Output pin 3 (from the second (or astable) 555 timer)
C -> IR LED -> 100k resistor -> +V

That provided a much stronger pulse, but I just want to be sure that is hooked up properly. ie. I'm wanting the IR LED to be pulsed at high currents, but not run at a high current continuously. Does that make sense? In this type of connection, it constantly has juice flowing to the anode/+. But... I guess it doesn't matter until it has ground applied (triggered via output pin 3 through transistor)

Eez dat right?

Thanks for all the help so far!
E -> Ground ==> OK, that's common emmiter
B -> Output pin 3 (from the second (or astable) 555 timer) ==> There should be a current limiting resistor between pin 3 and the base
C -> IR LED -> 100k resistor -> +V ==> 100K sounds to high

In the colector circuit (+v - R - LED - Colector - Emiter - Ground you may calculate the R as

R = (Vsupply - LED drop - transistor drop) / desired current

Knowing the collector current you may estimate the base current ([Ib = Ic / hfe] for linear operation, but you want to saturate the transistor so use something like [Ib = Ic / 50] to [Ib = Ic / 10]. With the bas ecurrent you can get Rbase.

dabnis

New Member
R = (Vsupply - LED drop - transistor drop) / desired current

Knowing the collector current you may estimate the base current ([Ib = Ic / hfe]
I understand that except for the "hfe" part. And is "Rbase" referring to the base resistor value?

Also, would 2N3904s work any better than 2N2222 in this case, as it relates to current values?

This is powered from a 9v battery.

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