Cheap DIY radio - RX and TX modules - RC Groups
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Jan 09, 2014, 06:35 AM
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Cheap DIY radio - RX and TX modules


Guys ... with ATmega328 arduino Mini for just 2.6$ ... we are opening the roof for cheap and cheapest DIY TX and RX modules.

Latest of my discovery is following: http://www.ebay.com/itm/251408381426...84.m1439.l2649

A RS232 200m CC1101 RF module for just 6$

Mainly I think to use this for "follow me" function ... feed by a GPS signal (on a airplane) ... data collected from a quadcopter with MultiWii for follow up.

Anyhow ... I did also discover this: http://www.ebay.com/itm/231086899725...84.m1439.l2649 ... a 6$ 1000m NRF24L01 module .. with a nice amplifier ... another candidate for a cheap TX module.

And ... what about these 3$ RF module: http://www.ebay.com/itm/380755147355...84.m1439.l2649

So .... opportunity are endless.

What is needed in my view is some clean and easy connecting diagram ... and some arduino code as TX and RX ....

Any experience on cheap DIY TX and RX is welcome ... maybe we can try to also organize all the available module here ... like:

https://www.rcgroups.com/forums/show....php?t=1954078

https://www.rcgroups.com/forums/show....php?t=1921870



EDIT:

Let's recap the target of this thread:
Objective ... share DIY radios made from cheap RF modules + cheap CPU boards.

The king of cheap CPU board is: Arduino Pro Mini 328 , available for less then 3$ shipped. So STM32 is out of context here, until a sub 5$ STM32 module will be available

RF Module:

Si4332 module -> start from 3.5$ (433MHz even without boosted power out should have almost 1km range) -> DIY Project here: https://www.rcgroups.com/forums/show....php?t=2114859
NRF24L01 module -> start from 1.3$, 5.5$ with boosted power out (good for DIY TX, for a DIY RX 1.3$ is perfect)
A7105 module -> start from 3$ , but need 11$ for a boosted power out version. -> DIY project here: https://www.rcgroups.com/forums/show....php?t=1921870
CC2500 module -> start from 5$, but need 11$ for a boosted power out version. -> DIY project here (not full success report so far) -> https://www.rcgroups.com/forums/show....php?t=1667453

RF module + CPU
CC1101 + xxx CPU for 6$ ,,, supposed to provide RS232 with a 200m range

Special module:
ATmega48 + NRF24L01 adapter and 3.3v regulator cost 3.8$ (originally a SPI to i2c converter) ... with a new firmware this could be a perfect PPM + RSSI module .. for PNP solution
Last edited by e_lm_70; Mar 01, 2014 at 11:40 AM.
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Jan 09, 2014, 01:39 PM
Registered User
HillbillyBrewer's Avatar
I have been playing around with those nrf24L01's for a while and they work really well. I have some with the onboard antenna setup with some PIR sensors around the house which communicate to a receiver inside. So far they are very reliable (and fast). They must to be powered by 3.3v.

I have used the 433MHz ones and don't like them. They work, but not as good as the 2.4GHz modules (for my purposes anyway).

Here is one of the easiest examples to understand wiring and arduino code for the nrf24l01:

http://forum.hobbycomponents.com/vie...hp?f=25&t=1317
Jan 09, 2014, 02:24 PM
Registered User
I used these modules for combat robots.

http://www.ebay.com/itm/1pcs-433Mhz-...item3cc7431824

They are very cheap and easy to use, just connect the transmitter to the Tx output of your micro and at the receiving end the micro Rx connects to the receiver.

At that time most everyone was using 75Mhz radios and the battle cage more or less looked like a Faraday box to 75Mhz so there was lots of problems for those radios. At 433MHz the wavelength was short enough to work very well.

These radios need a ground plane to work well, some transmitters may not even oscillate without a ground plane. The receiver range was anywhere from a few feet to 1/2 mile depending on the ground plane.

It is very important to have a balanced signal, there has to be the same number of '1s' as '0s'. If the signal is unbalanced the range will be reduced, or even not work. We used a scheme where the data was sent four times, every other data byte was inverted. While not fully balanced it was good enough.

If the transmitter is powered with 9 volts, the signal is fully balanced and there are proper ground planes the range is fully out of sight.

At the time combat robots had lots of rules for radios. They did not allow AM radios and were frantic about interference. I suspect the real problems had a lot to do with the long wavelengths of the 75Mhz radios and the steel cages. We did not tell anyone we were using OOK, even with the large bots. They would have gone nuts! In any case the 433Mhz radios worked very well in the battle cage. We also used 315Mhz and 418Mhz radios. The remaining people currently doing combat robots still have crazy radio rules.

If you look at the pictures of the radio set, the transmitter is a simple one transistor oscillator that is gated on and off with the input signal. The receiver is a simple two transistor 'super regen' radio with a comparator to generate the logic level output.
Last edited by mjsas; Jan 09, 2014 at 02:39 PM.
Jan 09, 2014, 02:55 PM
Registered User
Quote:
Originally Posted by mjsas
I used these modules for combat robots.

http://www.ebay.com/itm/1pcs-433Mhz-...item3cc7431824

They are very cheap and easy to use, just connect the transmitter to the Tx output of your micro and at the receiving end the micro Rx connects to the receiver.

At that time most everyone was using 75Mhz radios and the battle cage more or less looked like a Faraday box to 75Mhz so there was lots of problems for those radios. At 433MHz the wavelength was short enough to work very well.

These radios need a ground plane to work well, some transmitters may not even oscillate without a ground plane. The receiver range was anywhere from a few feet to 1/2 mile depending on the ground plane.

It is very important to have a balanced signal, there has to be the same number of '1s' as '0s'. If the signal is unbalanced the range will be reduced, or even not work. We used a scheme where the data was sent four times, every other data byte was inverted. While not fully balanced it was good enough.

If the transmitter is powered with 9 volts, the signal is fully balanced and there are proper ground planes the range is fully out of sight.

At the time combat robots had lots of rules for radios. They did not allow AM radios and were frantic about interference. I suspect the real problems had a lot to do with the long wavelengths of the 75Mhz radios and the steel cages. We did not tell anyone we were using OOK, even with the large bots. They would have gone nuts! In any case the 433Mhz radios worked very well in the battle cage. We also used 315Mhz and 418Mhz radios. The remaining people currently doing combat robots still have crazy radio rules.

If you look at the pictures of the radio set, the transmitter is a simple one transistor oscillator that is gated on and off with the input signal. The receiver is a simple two transistor 'super regen' radio with a comparator to generate the logic level output.

Ups .. the 1$ 433 modules ... I did not include intentionally ... they can be fine, but too much extra coding and extra care, and lot of fuzzynes

I order some of the item I post ad ebay link ... going to check the range soon ... also ... I would like to collect some link wth ready made arduino code for these modules ...

Jan 10, 2014, 08:17 PM
Registered User
Attached are some pictures of the low cost radio systems. The first picture shows the transmitter and receiver. They were intended to look like crap and mostly do. The transmitter has four buttons for the tank steer robot. Left forward, left reverse, right forward and right reverse. The buttons were carefully placed to fit the drivers hands. The is also two buttons on the back for the lift arm, up and down. Other buttons and switches were for the flame thrower.
The back side was covered with copper tape to make a ground plane. The wavelength monopole antenna is in the center. The receiver is in a box, the outside of the box was also covered with a metal foil for a ground plane.

The second picture is of four 1 pound bots we used for school demos. The is one transmitter with four control pads to control the four bots. The command bytes had an ID field so the receivers could sort out their commands.

The third picture is the inside of the small bots. It was powered by 4, 9volt batteries giving 18 volts to the motors.

The fourth picture is of several different receivers. On the left is a superhet receiver that had very long range.

The fifth picture is the transmitter board. It used an Atmel micro and could have up to eight input switches.

The last picture is the receiver. It had up to eight relay drivers that could drive 70 amp relays. It could also drive FET H bridges.

The code was pretty simple. We also had a receiver with a gyro for a two wheeled bot.
Jan 10, 2014, 09:41 PM
Registered User
Hello.
Im building an arduino based transmitter. You can check its at this url https://www.rcgroups.com/forums/show....php?t=1817699
Hope its helps you
Jan 10, 2014, 10:18 PM
Registered User
i suggest build with modul NRF 24l01 range is 1km , if you want to range far , you can use a booster 5km . it is great . Only buid once

modul 7105 ,C2500 is range very short and noise .

you see Project of medilic use a7105 because it only lucky Bind tx flysky. I do not appreciate this module

modul 315 or 433mhz is very bad, it is very very very noise , can't use for motor brushed. Don't think it
Last edited by fantasy1988; Jan 10, 2014 at 10:28 PM. Reason: o
Jan 11, 2014, 03:35 PM
Registered User
Check out the RFM50 module. The specs make that other stuff look like trying to use a tin can and strings to communicate.

They're $9.90 here...
http://www.d6labs.com/index.php/web-...90&id=10930770
Jan 11, 2014, 04:44 PM
Registered User
Quote:
Originally Posted by jakestew
Check out the RFM50 module. The specs make that other stuff look like trying to use a tin can and strings to communicate.

They're $9.90 here...
http://www.d6labs.com/index.php/web-...90&id=10930770
Nice one.

It could be a single module radio TX or RX , with 2 serial, i2c, maybe even more powerfull then an atmega arduino chip ... thr issur is to find development environment and some sample code for start ...

Jan 11, 2014, 07:24 PM
Registered User
It does have more processing power than most (maybe all) of the arduino chips.

3DR uses the same RF chip in their telemetry radio. And there is some example code floating around.
Jan 13, 2014, 10:18 AM
RC beginner
most of you should realize by now threads based on oddball chipset or development tools will languish. even if you dont plan on compatibility in the final version its a good idea to start out that way just to get your hands on cheap easy to find hardware and software tools.

24l01 is used in some early walkera toy heli products and modules are very common so not too bad. but obsolete now and not used in any current mainstream rc products. 2.4ghz coupled with 1mw output makes them shortest range of all. 100' if youre lucky.

those ebay 433mhz ook modules are super cheap ($1 for rx & tx) but not digital so unlikely to show up in any commercial radios. however the tx is capable of more power (1watt @12v) so have a couple advantages over all the others: cheap AND long range. specially if modified for fm. ive personally experienced los communication over several miles.

the popular rfm22b might be the best candidate so far for this thread. 433mhz and 100mw so pretty good range. its the heart of popular openlrs. now hobbyking carries many products based on it. and lots of adruino and other avr support which, lets face it, is the top dog in town as far as development platforms go.

so imo these are the only serious considerations for a cheap diy radio:

24l04: very short range and oddball protocols but low cost ($1) and easy to buy

rfm22b: medium range and $5 aint too bad. lots of support too.

ebay 433mhz: no rc protocols but cheapest and longest range of all.
Jan 13, 2014, 11:26 AM
Stuart
srnet's Avatar
Quote:
most of you should realize by now threads based on oddball chipset or development tools will languish.
.............
the popular rfm22b might be the best candidate so far for this thread. 433mhz and 100mw so pretty good range
.................
and $5 aint too bad. lots of support too.
There is the issue that the real cheap modules are real cheap because a lot of them are made to be used for all sorts of things, and they tend to be on a frequency that you would not want to be using for RC control in the first place, because its occupied by lots of those cheap radio modules already.

So a major requirement is to be able to choose to operate the radio on a frequency that is both legal and not subject to piles of interference, the RFM22B scores well here too.

Operate the RFM22B under 10mW, and it will give you plenty of range, and in a lot of places you can legally use it on a frequency of your choosing.
Jan 13, 2014, 11:45 AM
Registered User
I am thinking about using an Android tablet as both a controller and transmitter for controlling a bot. I would need to write an app to output the pitch and roll to bluetooth.

The forward/reverse speed would be controlled by the pitch angle and the steering would be the roll angle. Other functions could be controlled with either buttons or thumb swipes.

The first picture is a bluetooth to RS232 receiver that would be in the bot. A micro would convert the commands to PPM for the motor ESCs.

The second picture is a screen shot of a GSP test program that also shows the pitch and roll angles of the tablet. The compass does not read correct unless the tablet is level, otherwise the reading is totally wrong. The GSP does not work in buildings. I have not determined a use for the acceleration.
Jan 13, 2014, 11:55 AM
Registered User
Quote:
Originally Posted by mjsas
I am thinking about using an Android tablet as both a controller and transmitter for controlling a bot. I would need to write an app to output the pitch and roll to bluetooth.

The forward/reverse speed would be controlled by the pitch angle and the steering would be the roll angle. Other functions could be controlled with either buttons or thumb swipes.

The first picture is a bluetooth to RS232 receiver that would be in the bot. A micro would convert the commands to PPM for the motor ESCs.

The second picture is a screen shot of a GSP test program that also shows the pitch and roll angles of the tablet. The compass does not read correct unless the tablet is level, otherwise the reading is totally wrong. The GSP does not work in buildings. I have not determined a use for the acceleration.
I have / had tons of the RS232 bluetooth module ... they are all the same ... all with no more then 5m range from your tablet.

On Android tablet there are already PPM out application that make PPM signal from your ear phone jack

Jan 13, 2014, 11:58 AM
Registered User
Quote:
Originally Posted by dave1993
...
24l01 is used in some early walkera toy heli products and modules are very common so not too bad. but obsolete now and not used in any current mainstream rc products. 2.4ghz coupled with 1mw output makes them shortest range of all. 100' if youre lucky.
...


Quote:
Features:
This wireless Transceiver module is an easy and suitable module if
you want to setup your wireless communication system with low cost!!
It can achieve a good balance between wireless transition performance and cost!
You can easily add it with your own MCU/ARM/PIC/AVR/STM32 system!
What\'s more, this nRF24L01+ module is designed with Power amplifier and SMA antenna
This allowed you to use the wireless communication up to 1000 meters! (No barrier)
The module that I did link claim a 1000m range .. for 5.5$ price

I want to test it in conjunction with the cheap module ... use a power one as TX , and cheap one as RX .. let see what range I can get


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