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 Post subject: Guidance on building transmitter for a vintage game from 70s
PostPosted: Jun Sun 21, 2020 8:49 pm 
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Backstory: Helped a friend locate a vintage wall game called Tombstone by the Sunbird Corporation made in the early 70s. It looks like a big picture frame with a western scene on it. Bad guys (and good guys) are lit up with incandescent lamps. The original game came with (2) transmitters that are using RF wireless technology. This one has been retrofitted with wired "guns", and it looks terrible. We'd like to see this thing operating on the original design specs, but finding the wireless remotes has proven impossible. It's basically a reaction time game, and so pressing a button on the remote sends an RF signal to the game, which determines if you shot the bad guys or not.

Your reaction: Yeah, so what? How on earth can we help with that?

The good news is that I'm no stranger to soldering and basic electronics knowledge. I've built a few custom PCB designs previously. The best news? I have the Operation and Service Manual for it, complete with schematics. The printing overall is pretty good and 99% legible. What I need help with specifically, is understanding a few bits from the schematic and parts list. My understanding of the analog world is quite a bit more limited than the digital one.

There are a few terms in here that I haven't seen before, and Googling for them actually led me to this forum, so I thought I'd take a shot. Here's a list of questions I have:

    What is meant by the terms 3.0 KC and 5.2 KC?
    Does anyone know why coil/inductor L1 is listed as 40/80UH?
    Do the part descriptions "Audio Coil 23A682 RPC" or "OSC Coil 70F337AP" tell you anything useful about the coils themselves?

If you made it this far, thanks for reading! Is my request welcome here, or am I barking up the wrong tree?


Attachments:
File comment: Schematic
IMG_4669.jpg
IMG_4669.jpg [ 553.79 KiB | Viewed 1672 times ]
File comment: Parts List
IMG_4667.jpg
IMG_4667.jpg [ 610.48 KiB | Viewed 1672 times ]

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Mon 22, 2020 9:51 pm 
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Right, there are lurkers here who can read that mumbo jumbo.

KC or Kc could be kilocycles now known as Mega-hertz, Mh, but give us the context, the complete sentence where it was used.
Coils are measured in Henrys, so the term UH gives us a ballpark size of the coil. Micro-farads are written as Ufd, so
UH is micro Henrys.
Someone will correct me if any of this is wrong, so stay tuned. :lol:

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Mon 22, 2020 10:30 pm 
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KC usually means "kilocycles", or "thousands of cycles per second". Nowadays, it is preferred to be writen as "kilohertz", abbreviated "kHz". So, "3.0 KC" = "3.0 kHz" = "3000 cycles per second". "MHZ" stands for "megahertz", or millions of cycles per second. For example "1 MHz" is "one million cycles per second" which is equivalent to "1000 kHz" or "a thousand thousand cycles per second".

The parts list text is apparently for a receiver circuit. Your schematic is for a transmitter, so the two are not directly related. I surmise there are two transmitters for the game, one for a "good guy" and one for a "bad guy". Each "guy" operates on his own rf frequency. Because the schematic is a little fuzzy it's hard to make out the exact frequencies used. Perhaps one guy is 49.535 MHz and the other is 40.820 MHz. Just my guesses. Whatever the exact rf carrier frequencies are, the 49.xxx MHz transmitter modulates its carrier with a 5.2kHz sinetone. The other modulates with a 3.0kHz sinetone. The rf carrier frequency is generated by crystal oscillator Q3. The modulating sinetone frequency is generated by transistor Q1 and its frequency is determined by L1 with C1,C2. I'm a bit puzzled by this Q1 oscillator circuit. I don't see how it operates, exactly. Where is feedback to Q1's base? As to the 40uH/80uH question, neither value works out very closely to 3 kHz or 5.2 kHz using the c1, c2 values stated on the schematic. So, I'm going to leave it there for one of our smarter members to pick up with.

At any rate, another thing to wonder about is, the receiver parts list includes a 49.375 MHz crystal. So, how does this relate to the two transmitter frequencies? I will guess there are two receivers, one for each "guy". This way, both "guys" can transmit simultaneously.

As to your coil numbers, I don't know.

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Tue 23, 2020 12:08 am 
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Thanks for both of your responses! It's obvious I'm not a radio guy, as KC should have been immediately obvious to me now in retrospect. I have attached the correct parts list for the transmitter since I accidentally took a photo of one of the receiver's parts list.

If I'm not mistaken, the Q1 oscillator is activated when the switch pictured down by the battery is pressed. The top of the diagram shows it like 9V is connected all the time, which isn't true. It should only be activated when the momentary push button is activated.

You are correct, the game can be played with 2 players and there are two receivers in the game unit. Both are technically "good guys". But whomever presses the button first gets the credit for nabbing the baddie.

Does anyone know what the words "WHITE" and "YELLOW" mean in conjunction with the transistor part number 2N3395? (i.e. 2N3395-White and 2N3395-Yellow) I've actually seen reference to those colors in the part numbers in some Google searches, but nothing actually seems to indicate what the color names mean.

Thanks, everyone!


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File comment: Correct transmitter parts list
IMG_4672.jpg
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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Tue 23, 2020 1:03 am 
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Ah, okay, the "audio coil" L1 is an adjustable inductor. Range between 50 and 60 millihenries would be the minimum range, so perhaps the original was between 40 and 80?

No idea what the colors mean to us. Perhaps selected for an hfe range.

Quote:
It should only be activated when the momentary push button is activated.
Circuit snippet in lower left corner suggests this as well. C10,C11,C12,C13 are bypass caps whose physical placements are determined as much by pcb layout as anything. They certainly aren't stuck next to each other in a corner of the pcb!

edit: a range of 40-80 millihenries is very wide seems unlikely. A modern part will have nowhere near that. I found a 52mH Murata part with only a 7% range on a good day. That may be enough for operation at 3.2kHz with C1 and C2 values shown, but for 5.0kHz C1,C2 must be changed to 0.039uF

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Last edited by richfair on Jun Sat 27, 2020 2:05 pm, edited 1 time in total.

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Tue 23, 2020 1:21 am 
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richfair wrote:

No idea what the colors mean to us. Perhaps selected for an hfe range.



Yep, hfe.
Attachment:
2n3395.PNG
2n3395.PNG [ 16.76 KiB | Viewed 1614 times ]

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Tue 23, 2020 2:09 am 
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how are the 'retrofitted" guns wired in? Is it simly a momentary switch mounted in the gun? If so it may not be nessessary to reproduce exactly what was there before. You can probably surf the web and find a circuit with plans or modules that will replace what was originaly there.


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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Tue 23, 2020 2:24 am 
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lupin3rd wrote:
You are correct, the game can be played with 2 players and there are two receivers in the game unit. Both are technically "good guys". But whomever presses the button first gets the credit for nabbing the baddie.
My original interpretation tha there is only one receiver is not correct.

I just checked the transmitter schematic and it is correct that there are two different RF carrier receiver frequencies.


Last edited by LM386 on Jun Tue 23, 2020 2:46 am, edited 3 times in total.

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Tue 23, 2020 2:28 am 
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There you go! Thanks tbone8! Q1 oscillator's feedback is injected via its emitter while the base is held steady. I can imagine Q1 needs high gain to oscillate at all.

I wonder what the average current draw of this transmitter is? Schematic shows two 9v batteries in parallel. Looks like the Q2-Q4 modulator could draw hefty current (relatively speaking) from the batteries.

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Wed 24, 2020 4:21 pm 
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Wow! Thanks, everyone! So many good replies in such a short time period!

Okay, so now that I have my questions about the parts list out of the way -- if I want to start to build one of these guys from scratch, are there any guidelines about component distance for the coils or the caps that are displayed down by the 9V battery? In general, I'd try to keep everything as closely connected as possible (i.e. Avoiding long traces in general).

This schematic seems simple enough that I plan to use some spare breadboard that I have lying about, or possibly some of the prototype board that has solder pads on each hole.

Any tips you may have before I get the parts rounded up and start soldering would be appreciated. We're going to rebuild the original linear power supply soon, and I'm hoping to have the prototype built before then, as it would be amazing to see it potentially fully-working by that time. (Currently, the game works, but seems to have intermittent issues related to the original power supply)

EDIT: I did forget to ask if anyone has a recommendation for a good source to find the crystals I need. Specifically a 49.830MHz and 49.890MHz. I think I located one of them, but couldn't find the other -- was hoping somebody had a good supplier for common radio-specific crystals.

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Wed 24, 2020 4:35 pm 
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richfair wrote:
The modulating sinetone frequency is generated by transistor Q1 and its frequency is determined by L1 with C1,C2. I'm a bit puzzled by this Q1 oscillator circuit. I don't see how it operates, exactly. Where is feedback to Q1's base.

Q1 is operating in a common-base circuit. (The schematic could have been more explicit about this.) The feedback is from the emitter (output) back to the collector (input).

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Thu 25, 2020 7:19 am 
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stevebyan wrote:
richfair wrote:
The modulating sinetone frequency is generated by transistor Q1 and its frequency is determined by L1 with C1,C2. I'm a bit puzzled by this Q1 oscillator circuit. I don't see how it operates, exactly. Where is feedback to Q1's base.

Q1 is operating in a common-base circuit. (The schematic could have been more explicit about this.) The feedback is from the emitter (output) back to the collector (input).

Shouldn't there be a capacitor from Q1's Base to Ground?


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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Thu 25, 2020 3:25 pm 
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Quote:
a recommendation for a good source to find the crystals I need. Specifically a 49.830MHz and 49.890MHz. I think I located one of them, but couldn't find the other -- was hoping somebody had a good supplier for common radio-specific crystals.
Those are some of the common numbers from unlicensed citizens band frequencies. Think walkie talkties. Maybe you can score them from used/broken sets at yard sales or ebay (yeah, it takes opening them up and hoping to find what you need). You might consider available new crystals that are in the unlicensed 49MHz range and change out the receiver crystal(s) to match new transmitters. It would probably require peaking the receivers for optimum operation but would be a lot easier than another option of building a frequency sythesizer into each new transmitter.


Quote:
Q1 is operating in a common-base circuit. (The schematic could have been more explicit about this.) The feedback is from the emitter (output) back to the collector (input).
I don't quite grasp this but perhaps if I breadboard the circuit I can see and learn. I had thought a common base bjt circuit responds to "input" between emitter and base (signal common is at the base lead), and gives "output" between its collector and signal common. This is an oscillator not a straight amplifier and the phase shifting by the LC tank confuses things in my head. But I'm still thinking as if the oscillator's actual output is from the collector which is phase shifted through the tank (necessary for oscillation) and is fed back to Q1's emitter, and simultaneously passed along to Q2. The feedback "wiggles" the emitter potential, which also affects the bjt base-emitter potential, and THAT is how feedback gets to the base. In such a case, I would think a capacitor from base to ground would help a Q1 with lower hfe to oscillate. But...
It is entirely likely I am horribly confused and therefore hope you can explain how this oscillator works.

I don't want to hijack the OP but hope this is relevant to his build plans.

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Thu 25, 2020 9:55 pm 
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Okay, some of your suggestions have me thinking a little more closely about the build. Originally, I was thinking it would be great to rebuild from the ground up, per the schematics, but I'm having trouble with sourcing a few parts. I will probably see if I have some walkie talkies around the house that might have what I need crystal-wise. However, I'm still left trying to find the 2N3395 (White & Yellow), and most of what I find in that regard are just generic NTE cross-refs, and the hFE specs don't seem to match.

SO...

Remaining questions: Are these transmitters even a good design? Is there anything that jumps out as obnoxious about the schematic or design itself? Since it is known what the output frequency and relative amplitude should be, does it even make sense to try to build this as-it-was, or would it be easier to create a modern RF transmitter using a simplified design with parts that aren't unobtanium? Or will making a modern compatible transmitter still force me to source the identical parts in the original design (crystal and transistors)? I suppose the crystals are non-negotiable, unless I can modify the receivers to match.

The recommendations to swap out crystals with easier to find alternatives is quite appealing, but since I don't have a radio background, it seems like shoring up the receiver to match might be more than I can handle. My radio theory knowledge is pretty low, so I've been trying to Google my way into a basic understanding of the fundamentals.

This page has some ideas, but is light on theory or anything that helps a novice radio pupil to understand.

Maybe it's helpful to state the aim of reproducing the transmitters in the first place. The wired guns look bad, as they are from a modern arcade gun game. The original used "garage door" style remotes, which don't necessarily look very cool -- but the philosophy I'm adopting here is "to make some remotes that function in the same way as the original." They don't have to be part-for-part exact, but they should be wireless and use the same technology. As-is, the machine is wired in a way that I think the receiver boards are bypassed altogether, which to me is a deal-breaker. The parts on the machine should be doing their job. I'm just trying to re-create or mimic the wireless pieces that are missing without "undoing" too much of the original design.

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Fri 26, 2020 1:16 am 
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LM386 wrote:
stevebyan wrote:
Q1 is operating in a common-base circuit. (The schematic could have been more explicit about this.) The feedback is from the emitter (output) back to the collector (input).

Shouldn't there be a capacitor from Q1's Base to Ground?

You're quite right, I'm mistaken. It's a common-emitter amplifier, with shunt feedback (and no input signal :-) )

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Fri 26, 2020 1:31 am 
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richfair wrote:
Quote:
Q1 is operating in a common-base circuit. (The schematic could have been more explicit about this.) The feedback is from the emitter (output) back to the collector (input).
I don't quite grasp this but perhaps if I breadboard the circuit I can see and learn. I had thought a common base bjt circuit responds to "input" between emitter and base (signal common is at the base lead), and gives "output" between its collector and signal common. This is an oscillator not a straight amplifier and the phase shifting by the LC tank confuses things in my head. But I'm still thinking as if the oscillator's actual output is from the collector which is phase shifted through the tank (necessary for oscillation) and is fed back to Q1's emitter, and simultaneously passed along to Q2. The feedback "wiggles" the emitter potential, which also affects the bjt base-emitter potential, and THAT is how feedback gets to the base. In such a case, I would think a capacitor from base to ground would help a Q1 with lower hfe to oscillate. But...
It is entirely likely I am horribly confused and therefore hope you can explain how this oscillator works.

You're right to be mystified, I was mistaken. It's best analyzed as a common-emitter configuration with shunt feedback to the emitter resistor, as you have done in your reply.

I also confused the "output" of the oscillator with the output of a common-base configuration - if it was operating common-base, the input and output would be the opposite of my post, as you have pointed out.

At resonance, the parallel tank circuit is a very high impedance, so the gain is quite high despite the degeneration from the emitter resistor.

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Fri 26, 2020 3:47 am 
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The circuit is a Colpitts oscillator of which there are a number of variants.

It should have a capacitor from Base to Ground.

https://wiki.analog.com/university/cour ... lpitts-osc

http://fourier.eng.hmc.edu/e84/lectures/ch4/node12.html

https://www.indiastudychannel.com/resou ... lator.aspx


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2b3b800cb233c131b5aba8ed3ff3abeb.gif
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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Fri 26, 2020 7:46 am 
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LM386 finally nailed the audio oscillator.

It may work with just the resistors on the base. A capacitor would certainly increase the gain.

Now on to the RF oscillator. Has anyone mentioned the missing connection at the collector of Q3? Has to go to the choke, L2, and one end of the crystal.

I think the transistors were early GE TO-98 parts. Many different newer TO-92 parts should work OK. Watch out for the pinouts, though. The bulk of TO-98 parts had the collector lead in the middle. I would just try whatever is in the junkbox.

The difficult parts are probably the coils. Those look like Newark stock numbers. Does anyone have a 1967 catalog handy?

You might find a starting point for the RF coils by borrowing from a 6 meter ham radio design. An audio driver transformer for a transistor radio might work for the audio oscillator.

TEd

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Fri 26, 2020 3:01 pm 
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Sorry to be Debby Downer but I think you’ll need some local help to pull this off unless your skill set is more advanced than you have let on. At this point I would have to recommend you look for someone to partner with locally such as a ham radio enthusiast or perhaps a nearby member of this forum.

The original schematic has low parts count which makes it appealing, and I agree that it is desirable to keep the game’s original rf receivers if possible. And it is possible. Making new, small, remote transmitters will require time, effort, and probably some experimentation. Transistors can be substituted of course which may require other circuit changes.. It is likely there are one or more errors in the schematic, especially the Q3 collector’s lack of DC supply path as noted above. (edit add: Could the omission actually be intentional to force only a short burst of rf carrier no matter how long the button is held? Prob. not.) Is L2 connected properly and what is its value? At minimum you should have a DVM or other suitable meter and an oscilloscope and some knowledge/guidance about what changes to make, what waveforms to look for and where, and how to interpret what you see when trouble appears. A frequency counter to verify sinetone and rf frequencies would be much handier than just the 'scope. BTW how do we know the receivers work? We don’t and cannot test them without building a transmitter that broadcasts the proper signals.

Building the Q1, Q2 “audio” oscillator portion is trivial if you have the exact “audio coil”, which you do not. You can substitute an adjustable coil that is within the range of interest (a 52mH part is available, see earlier post about C1,C2 changes at 5.0kHz) or perhaps wind your own, OR a different adjustable oscillator design could be adapted. The Q3, Q4 portion is more needy. Any rf circuit’s performance, including these transmitters, will depend on physical component placement and pcb trace routing to work well. Bypass capacitors, like those gathered into the schematic’s corner, will likely be needed at specific circuit points to prevent the 49MHz signal that radiates everywhere from causing trouble. We can make guesses about those circuit points but the physical layout is part of the consideration. Experimentation will probably be needed once real pcbs are built. Also, the remote’s internal antenna loop probably should be a specific length to be an efficient-enough radiator, and the Q3 circuit must be tuned to it. Once working, receivers can be checked. They may need repair or at least adjustment. It is a lot to ask of yourself without prior rf experience.

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Last edited by richfair on Jun Sat 27, 2020 2:16 pm, edited 2 times in total.

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 Post subject: Re: Guidance on building transmitter for a vintage game from
PostPosted: Jun Fri 26, 2020 3:15 pm 
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(I had to break previous post into 2 parts due to odd formatting problems when posted into single long post.)

It would be possible to find some old remotes and adapt them, maybe. The 49MHz band is rarely used for remotes today but it was all the rage a few decades ago, for garage doors, fan and light dimmers, etc. You’re still stuck finding crystals of the proper frequencies (possibly pairs if not the original frequency crystals) but at least the transmitter+antenna portion would be proven to work. Some homebrew skills would be required to adapt and incorporate the audio sinetone oscillator into them.

This morning I saw an ebay listing for a used wireless microphone transmitter/receiver that claims to operate at 49.830MHz. The crystals may be just right for you and price not high. I also saw a listing for a “new in box” wireless microphone that claims to operate on either 49.830MHz or 49.890MHz. Does that imply two sets of crystals or some other scheme? I don’t know and I wouldn’t spend the asking price to find out. Even with the proper crystals, you have to attack all the actual build challenges.

Since you have not yet posted the receiver or other schematic parts, we still don’t know exactly how they operate (why are different audio frequencies used for each remote?) and we’re making assumptions based only on the transmitter schematic. Never assume anything! I still note a difference in crystal frequencies on the transmitter schematic and receiver's parts list.

Finally, there is a conceivable huge downside to adapting a modern rf “keyfob” type of transmitter/receiver kit in place of the original transmitters and receivers. Time delay! Whereas the original circuits will respond very quickly after pressing the button, key fobs require a digital code to be serially broadcast, often repeatedly while the button is pushed. The receivers screen out random static and noise by waiting for a signal they can decode, and after verifying then send an “unlock” signal. There may be a significant delay time (perhaps 10s of milliseconds) between initial remote button push and the receiver’s “unlock” signal change. Time delay is not what you want to build into a game of reaction time.

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