# Cheapest and simplest remote control

#### Kenny

Joined Oct 11, 2004
55
I need the cheapest remote control (not IR) that counts with, only one button, about 100m span range, and being able to send an unique code different of another equal unit.
I need to have 300 of them working almost simultaneously.
And with a central unit connected to a PC (with a software made by me) reading all of them and identifying what units were button pressed.

Then, do you know some ready made product that meets the specs.
Or can you tell me what is the simplest design on what I can begin to work?

#### praondevou

Joined Jul 9, 2011
2,942
Linx Technologies have some nice "data in - antenna out" encoders/transmitters. I just bought a few of THESE at futureelectronics. But they are a bit expensive and the fact that your 300 units have to work simultaneously sounds like a problem to me.

#### Kenny

Joined Oct 11, 2004
55
Thanks for your reply . I checked the link, the modules seem very interesting. But I checked the price on futureelectronics of the eval kit and is very very expensive for my needs (U$115), although I don't know the price per module. I want to make clear some things . I have in mind simple remote control units: price around U$5-10 with the capability of send a pair of bytes at a touch of a button, identifying exactly the uniqueness of the sender, differentiating from the others. And the receiver being capable of process 300, not exactly simultaneously, but not collapsing on the process.

I don't know, maybe you know and understand more about it. And can give me something more to see. For example, I thought initially on remote controls on the KHz band...

#### thatoneguy

Joined Feb 19, 2009
6,359
Until you get to the "multiple" at the same time, the requirement isn't that hard.

You will need to use more than a few frequencies.

Imagine your chosen frequency is the color red for a second.

When one Red LED blinks, you can read it easily. When 100 blinking LEDs are blinking, all you see is red, and can't make out exactly which one is blinking.

Same goes with RF, only one signal can be modulated on a frequency at a given moment, unless you are multiplexing, but since these are individual units, that is removed as an option.

The only multiplexing left is time, such as the system Ethernet uses. Collision Detection Multiple Access. Every sender needs a receiver as well, if it senses a transmission, it needs to wait until the transmission is over, then send.

Give each unit a timeslot in which to transmit, though clock sync would be difficult.

Last option would be polling, giving each transmitter an address, and the master Tx/Rx rapidly polls each address, and if there is data to send, the button Tx/Rx sends it, if no data, the Tx/Rx returns a no data code (or it's battery level). This would ensure all remote buttons are "alive" as well.

All of them would be a headache to implement once "multiple" is put into the requirements.

#### Zazoo

Joined Jul 27, 2011
114

I think the whole thing including an additional uC and PCB would cost less than $10/unit. http://forum.allaboutcircuits.com/NRF24L01-2-4GHz Thread Starter #### Kenny Joined Oct 11, 2004 55 Thanks to all. That explanation with the red color is very good , and the options for multiple also. With the linx modules named above, or alike, it seems to me that the possible solution is polling. Is needed to calculate how much time take to read the same first unit, giving the round. I ask : is quantity at the same time a limitation of the implementation of RF technology? and that is the reason of the existence of modules like Xbee? Well, guessing that I can get a solution of multiple, what modules can be the cheapest and simplest, with one button, U$5-10?

OTOH, how does it work the alarm's car, because seem that don't have this multiple problem. i.e. in a parking many people activate the alarm and each car responds fine without interfering with the other. Are all the alarms's cars tuned to very different frequencies and protocols, and what if multiple cars have the same mark of alarm?
Many thanks for make clear all of this to me.

#### praondevou

Joined Jul 9, 2011
2,942
Well, guessing that I can get a solution of multiple, what modules can be the cheapest and simplest, with one button, U$5-10? I doubt you'll find an off-the-shelf solution for$5 to $10 / unit.You'll probably need to do it yourself. OTOH, how does it work the alarm's car, because seem that don't have this multiple problem. i.e. in a parking many people activate the alarm and each car responds fine without interfering with the other. Are all the alarms's cars tuned to very different frequencies and protocols, and what if multiple cars have the same mark of alarm? Many thanks for make clear all of this to me. Car alarms can work on several frequencies, i.e. 315MHz, 433MHz, 868MHz etc. I doubt that if 300 people would try to activate/deactivate their car alarm at exactly the same moment there wouldn't be any problems/interferences. It works because not everybody is activating his key at exactly the same moment, and if there is interference people would try to press the button again on their remote control. Also the distance / transmitted/received power is different for each participant. You can't compare a parking lot with what you try to achieve. Unless you find an off-the-shelf solution I don't see how to do it without some programming. You can get it done for less than$10 as I described above.

#### Kenny

Joined Oct 11, 2004
55
Of course your answer above is very very good. Just that I saw it later after my post (I was writing it, while you post yours)
I like the latch register idea and also I checked those modules on ebay (I will try them, but some doubts, they need antenna? i see the same module http://www.sparkfun.com/products/691 with antenna but at high price, and in general what is the difference on distance range of RF transceiver modules with/without antenna?)

I've good programming experience, maybe not much on mCU, but surely enough. Then I'm going to think and design

However, if there is a ready made control much better, one problem of my own design is to achieve a proper case, you know something that looks professional to the pretended client.

OTOH A couple of questions more:
What you would need are transceivers (receiver with transmitter). The ones from Linx are too expensive. If you have a look at digikey.com you'll see that the cheapest transceiver chips are about $3 to$4. But the need a good amount of external components too, at least a uC or encoder/decoder. But even with those it should be possible to do it for less than $10. I actually bought transmitters with integrated encoders from Linx, but I used only encoder/decoders in conjunction with the MICRF112 and MICRF022 from MICREL for now. All these ICs are really easy to use, not like a few decades ago. Even people unexperienced with RF can implement them very easily. Their frequency stability is also very good. . Do you have some specific resource (book, tutorial, not google ) Sorry I don't I would have to search it too. (on Google) As for the case the electronic distributors like digikey, futurelectronics, avnet etc all offer different cases, you would have to look through it. As I just learned here on AAC if you are looking for a specific part goto "findchips.com" they check several distributors for you. I suggest you first decide what distance you need, how fast you need to recognize a button press and other details etc. Thread Starter #### Kenny Joined Oct 11, 2004 55 These are 2.4GHz modules, the have a small PCB antenna onboard It means at this frequency the communication doesn't need a large antenna, is totally working with a small integrated antenna? What you would need are transceivers Oh yeah of course, but how much is expensive? just for curiosity. All these ICs are really easy to use, not like a few decades ago. Even people unexperienced with RF can implement them very easily. That is the reason I like to know how are made this kind of things some time ago, simple radio transmitters, from the ground basis. Not for this project. But I think today everything with very specialized chips and software is too much easy . I suggest you first decide what distance you need, how fast you need to recognize a button press and other details etc. I'm on it. And I'll check your useful links. It is very sound the idea of the control with no marks or alike. Just a beginner question how can I receive its signal, frequency, protocol, ... #### thatoneguy Joined Feb 19, 2009 6,359 Scanning 300 electronically, with maybe 2 bytes each, would happen in an eyeblink or two, not into the seconds realm. Depending on the requirement sheet for setup time before transmit, such as for a game show, etc, hit the button once and they will "listen" for an hour or whatever time period you decide. During that hour, they would wait to be polled by the master transceiver, which would decide who pressed first, etc. Run on a single CR2032 cell, or if 5V is needed, 2CR2032 cells + Diode. PIC or AVR processor, I like PIC due to nano-power sleep, takes less current than a CR2032 self-discharge does, so would be good for years. Sending the battery level or just the device ID back would be sufficient, then the button goes back to listening for it's address to be called next, maybe doing an ADC conversion on battery in the meantime to send every 10th query or something. After 1 hour of inactivity/being polled, the buttons would shut themselves off into deep sleep. Car alarms work with multiple frequencies and a "rolling code", so there is encryption and frequency pre-planned for the next cycle. The odds of more than 2 or 3 requests at the _exact_ same time are very low, and even then , garbled signals are ignored,. What do people do when their car doesn't unlock on the first try? Assume they didn't press hard enough and push the button again. (See CDMA as related to Ethernet Above) #### R!f@@ Joined Apr 2, 2009 9,747 Umm Kenny, Would u mind updating ur profile or telling us where are u from ? I could use ur help with a software design, that is if you do programming.. #### praondevou Joined Jul 9, 2011 2,942 It means at this frequency the communication doesn't need a large antenna, is totally working with a small integrated antenna? It looks more like a (probably not very effective) loop antenna. Wave length at 2.4GHz is 12.5cm. The antenna is apparently shorter than even λ/4. Oh yeah of course, but how much is expensive? just for curiosity.$17/transceiver

That is the reason I like to know how are made this kind of things some time ago, simple radio transmitters, from the ground basis. Not for this project. But I think today everything with very specialized chips and software is too much easy .
I agree it's easier, but I don't think it's EASY.

#### Kenny

Joined Oct 11, 2004
55
Many thanks to all of you for introduce me in the way of RF.
I wish finally can build this project. I'll begin to think, design, prototype.
I know that some of you can build this quick, but I'm bit slow, I like to learn many things for background before and also this is a project second to my real work. But, you can be sure that all that you teach me is totally valuable and I plan to put it on practice from now.

Just for finish (at the moment ), I don't understand all that you say about sending the battery level, the purpose, like this
thatoneguy said:
maybe doing an ADC conversion on battery in the meantime to send every 10th query or something

#### thatoneguy

Joined Feb 19, 2009
6,359
Many thanks to all of you for introduce me in the way of RF.
I wish finally can build this project. I'll begin to think, design, prototype.
I know that some of you can build this quick, but I'm bit slow, I like to learn many things for background before and also this is a project second to my real work. But, you can be sure that all that you teach me is totally valuable and I plan to put it on practice from now.

Just for finish (at the moment ), I don't understand all that you say about sending the battery level, the purpose, like this
In larger installations, a master controller of several remote devices wants to know if there is a low battery before it loses communication with the device entirely.

An example to easily understand would be the little pagers waitresses have, and some people in line get, at restaurants. The control board will see a low battery alert if it is a 2 way type. Another example are go-kart speed controllers at kids racetracks, if nothing else, send battery level. It's just a "frill" that is added on for marketers to to get clients happy about, or industry floor managers to think they'll monitor better, etc.

This is used when the receiving device needs to reply with an "alive" or "triggered" response, such as in a wireless alarm system for another example. Don't add two-way just for battery level, use an LED, but if you are already using 2 way, and have to reply, battery level is some useful data to reply with other than "present and working".