best sensor type for Wireless contest buzzer

Thread Starter

adolfoe

Joined Feb 11, 2019
5
Hello,

I am considering a project for my gf.

She is a teacher, and saw a project with 6 wireless buzzers, when pressed the buzzers a light tower indicates with a color scheme what buzzer was pressed first and what buzzer was pressed second.

I want to built something similar (I am not sure if the final project will use Arduino or a simple microcontroller for price saving).

Currently I want to use arduino for prototyping.

I was told that I could use these type of transmitters: https://www.ebay.com/i/392145706685?chn=ps, and that I should simply purchase one pair of transmitter-receiver for each sensor, but I am not sure if each pair is uniquely matched or not.

The other option I was considerring is using a 2.4GHz tranceiver like the NRF24L01, and have each buzzer transmit on a different channel, but I don't know if there is any transceiver that can detect tranmissions from multiple channels and the poll wich chanel sent the transmision first.

Do you have any suggestion.

Best Regards,
Adolfo Sanchez
 

sghioto

Joined Dec 31, 2017
2,405
I was told that I could use these type of transmitters
Correct, technically you would only need one receiver as each transmitter will be encoded with it's own identification code from the arduino. The receivers and transmitters are not matched other then they transmit and receive on the same frequency. These modules will work but only one transmitter can send data at a time.
Also look into the HT-12E and HT-12D series of encoders and decoders that will work with these modules allowing you to match the units without a mcu.
SG
 
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Thread Starter

adolfoe

Joined Feb 11, 2019
5
My understanding is that I should transmit a sort of unique ID for each buzzer pressed, and the receiver should detect what transmission arrived first.

But on this case, if I have two groups pressing two different buzzers within a small time interval, I could have interference and the receiver will be confused?

Can you provide an advice about how can I avoid this situation?
 

Thread Starter

adolfoe

Joined Feb 11, 2019
5
By the way, I would like to create a cheap prototye of this using scrap parts, was thinking of an old RF car keys, but I do you know where could I get a receiver on a scrap component?
 

sghioto

Joined Dec 31, 2017
2,405
My understanding is that I should transmit a sort of unique ID for each buzzer pressed, and the receiver should detect what transmission arrived first.
Yes but the receiver module would require additional circuitry to do the polling probably using the mcu.
if I have two groups pressing two different buzzers within a small time interval, I could have interference and the receiver will be confused?
Can you provide an advice about how can I avoid this situation?
Each unit would only need to transmit for about 100ms, avoid pressing buttons at the same time is one option. Another option is to have each unit on a different frequency or have a circuit or programming priority that only allows one transmission at a time.
SG
 

sghioto

Joined Dec 31, 2017
2,405
By the way, I would like to create a cheap prototye of this using scrap parts, was thinking of an old RF car keys, but I do you know where could I get a receiver on a scrap component?
I don't why you would want to considering the low cost of those modules and they would be a lot easier to prototype.
SG
 

pmd34

Joined Feb 22, 2014
520
You could use something like this:

https://www.aliexpress.com/item/5pc...lgo_pvid=bd954aa3-ad2f-49b2-bc37-fa4cc0059b06


Which already has encoding built in. (Others are available.. search "RF encoder" - you could use e-packet for faster delivery). As a previous reply commented you just need to make sure that when someone presses a button, it only "fires" for a short time, so there is no problem with overlapping signals.

If you are looking to build from scrap parts, I would look for some of those radio controlled mains / outlet sockets, these actually use the same type of 433MHz receivers. eg:
https://www.amazon.co.uk/Energenie-Radio-Controlled-Sockets-Gift-white/dp/B003GSPOFO
 

MisterBill2

Joined Jan 23, 2018
9,551
If you are using an RF link you need to consider latency, the delay between hitting the button and the logic portion receiving the input. If two or more kids hit their buttons at almost the same time then what will happen? With a single receiver and no limitation on the length of the transmission the first signal will prevent the rest of them from being sensed. So it may be that you actually need multiple receivers. That is a consideration that needs to be considered. There are work-arounds but they are not trivial.
 

Thread Starter

adolfoe

Joined Feb 11, 2019
5
Hello MisterBill2, yeah, I have already considered the option of using multiple transmitter-receiver pairs, but the issue is that I have not been able to find one product that adjust to my needs, all the RF receivers that I have searched, seem to be universal, that will receive data from multiple transmitters.

Can you suggest any model(s)?
 

MisterBill2

Joined Jan 23, 2018
9,551
Hello MisterBill2, yeah, I have already considered the option of using multiple transmitter-receiver pairs, but the issue is that I have not been able to find one product that adjust to my needs, all the RF receivers that I have searched, seem to be universal, that will receive data from multiple transmitters.

Can you suggest any model(s)?
Probably not Bluetooth or WiFi, for exactly those reasons. The really cheap RC toys that just have one control function could be an alternative, except they would probably be all on the same frequency. That is where wired controls have a big advantage, plus not losing the remote station buttons, nor having batteries fail. But tghere may be other items available in the 49 megahertz band, which presently is where the cheap radio control stuff is found.
OR, if you could rig each transmitter to only send a brief message, and disable after the acknowledgement, thatcould work. BUT it will be a lot more complex, probably.
 

Ioannis66

Joined Nov 7, 2012
44
If it must be wireless, then the only solution to trust would be a pair of tx-rx on different frequencies. So, if 2.4, Bluetooth are not available, consider Radiometrix modules that can be programmed on different frequencies.

But, unfortunatelly, all these solutions have a considerable delays in transmitting, receiving and decoding. So after pressing the button even 0,5 sec delay may be observed.

I'd use cable and get done with it.

Ioannis
 

MisterBill2

Joined Jan 23, 2018
9,551
If it must be wireless, then the only solution to trust would be a pair of tx-rx on different frequencies. So, if 2.4, Bluetooth are not available, consider Radiometrix modules that can be programmed on different frequencies.

But, unfortunatelly, all these solutions have a considerable delays in transmitting, receiving and decoding. So after pressing the button even 0,5 sec delay may be observed.

I'd use cable and get done with it.

Ioannis
the additional advantages of using a wired system are that there are no separate battery packs to keep charged and also that none of the remote devices will get lost, which is often a big problem. In addition, a wired system will not be subject to interference, it will be far less complicated, and it will cost a lot less. For a wireless system you will need 6 transmitters each with a unique signal, and either a six channel receiver or six receivers. That is a complex package in itself. So while wireless is "really cool", having six channels that respond without delay is not simple.
 

MisterBill2

Joined Jan 23, 2018
9,551
Six of the cheap one-button remote control toys could provide what you need, possibly, BUT finding six with different frequencies that did not interfere with each other could be a problem.
 

PhilTilson

Joined Nov 29, 2009
99
Given the valid objections that have been raised so far, how about this idea...

This would assume that the transmitting buttons (or at least, the transmitters) could be fixed securely to the desk or table that the student was sitting at. The transmitter consists of a block-mounted laser pointer, controlled by a push-button. These lasers fire instantly - no warm-up time. The 'receiver' is a small cabinet containing six phototransistors connected to your μC. When setting up, each laser pointer is targeted at its own sensor. That's it!

No problems with interference between transmitters. Easy interface to the μC and no need to worry about how long people press for or two people pressing at once. I am assuming that the whole idea is a kind of quiz game and whoever presses first gets to answer.

Thoughts?
 

MisterBill2

Joined Jan 23, 2018
9,551
Given the valid objections that have been raised so far, how about this idea...

This would assume that the transmitting buttons (or at least, the transmitters) could be fixed securely to the desk or table that the student was sitting at. The transmitter consists of a block-mounted laser pointer, controlled by a push-button. These lasers fire instantly - no warm-up time. The 'receiver' is a small cabinet containing six phototransistors connected to your μC. When setting up, each laser pointer is targeted at its own sensor. That's it!

No problems with interference between transmitters. Easy interface to the μC and no need to worry about how long people press for or two people pressing at once. I am assuming that the whole idea is a kind of quiz game and whoever presses first gets to answer.

Thoughts?
Only one problem with that approach is that school desks move around a lot, at least in every school that I have seen. But certainly laser pointers could be simple and fast transmitters, and a phototransistor would be a fast receiver. The one problem would be aiming. Now if the laser pointers, or some other cheap laser devices, were each modulated with a different frequency then there could be one larger target that all could easily hit. Tone decoders are easy and simple and could handle the signals with very little delay. I considered the option of tone modulated RF links but multiple tones could cause unexpected results, I think. That is why I did not suggest that concept.
 
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