Understanding radio system receiver

[magester1]

Hello there.
I'll start with a bit of personal history. A few years ago I started building aeromodelism planes and soon wanted to try something with motors and stuff. So I bought a Hitech Flash 4 radio system, maybe not the best but it was good enough back then. Unfortunately, I never used it at all.
I now want to use it for something, anything, even turning on and off a LED or driving a motor, anything at all.

So I wanted to understand how the receiver (HFD-08RD) sends the signals to the servos, since I'm not going to use them when its easier to connect the wires directly.
I'm not sure if it works with a certain frecuency, maybe PWM or just by changing voltage. I checked with a multimeter and got 0.25V when centered and about 0.12V difference when using a channel.

I hope this is the correct place to ask, since I am not going to use it in planes, I want to understand how it works to use it with other circuits or projects of mine later on.

Thanks for taking the time to read this.

 

[Sceadwian]

It's a PWM signal so your meter won't tell you much of anything useful. It's a simple signal that repeats 20 times per second (approximatly) The pulse for for left is 1ms long the pulse for right is 2ms long 1.5ms is center.

Unfortunately I can't condone the use of an aircraft transmitter for land based hobby type projects like this, because first of all it's illlegal. Second of all you may end up shooting down someone's aircraft operated up to a couple miles away if the circumstances are right, so for respect to other hobbyists out there don't do this. If you want to use an RF transmitter/receiver purchase one on the legal license free bands such as the units from sparkfun.com (which can be quiet cheap)

 

[magester1]

I thought it was PWM, thanks for clarifying that.
Now, I didn't know that it was illigal, I really didn't. However, I'm not sure if it's an aircraft transmitter only, I thought it was a general purpose one.
Regarding the frequency, I don't think I'll have a problem with other hobbysts since I purchased a new crystal making sure it's in the range people still don't use. Besides, there's only one place where aeromodelist hobbysts get together and it's far from where I live.

Anyway, thanks for answering so quick. I appreciate it.

 

[Birdman Adam]

Whenever I have needed to turn off/on something remotely around my house I've used 27 or 49 Mhz transmitters and receivers from cheap RC car toys. They provide up to five on/off channels. I amplify them so the signal goes about 100 ft (good for in house).

 

[Sceadwian]

72mhz band is aircraft only, 75mhz band is ground based vehicles only. They are for remote control vehicle use only general purpose use is not allowed. The transmit power is around 3/4s of a watt so the range under varying conditions can be further than you intend.

 

[magester1]

Birdman Adam:
That is a good idea, but the thing is... since I already bought this radio system I want to use it for something. If not it would just be a waste of money.

Sceadwian:
I guess I should have read more about all this anyway.
I'm still positive I'm not within range, farther than 10km.
So, your advice would be to either use it for an airplane or just get a new one, is that right?

 

[Sceadwian]

Yep. That would be my recommnedation. There are plenty of short range RF solutions out there. All of them, even modifying the one you have are going to require some vested interested in learning electronics.

 

[magester1]

I guess I'll stick to that then.
However, I'd be interested in what you have in mind for modifying it.
Besides, I am interested in electronics. I'm currently studying electronic ingeneering, started only a year ago though...

 

[magester1]

I decided to listen to you Sceadwian, I'm going to use the Radio for aircrafts.
I would still like some advice though.

Lets say I use the signal the receiver sends to the servos. If it's a 1ms to 2ms PWM signal, how can I make that a 0% to 100% PWM?
I've been looking for that and found some solutions, however they were kind of complex and required ICs I can't get. Is there any simple way of doing that? It doesn't need to be perfect or anything, just enough to "function"...
If not, could I interprete the signal as a 0 to 5 (or more) volts? I'd then work my way around that.

 

[Sceadwian]

The simplest way of doing it would be using a micro controller. It can easily read the 1-2ms signal and output 0-100% PWM.
Micro controllers are extremely powerful but again require a decent amount of time to get into using them, and you have to be able to or willing to learn how to program at the very least in Basic.

You're going to run into the same issue doing it with analog or discrete logic IC's as you would dong it iwth an electronics controller, you need to learn what you're doing before you can get desired results. You obviously have the curiosity which is great, but you have a lot of learning to do if you want to be able to do this for yourself, and having someone else do it really doesn't teach you anything, and generally it's not something another person wants to do, so it depends on how much time and effort you decide you want to put into this.

Controlling hobby servos is a very good project and there is a lot of documentation and circuits out there to help you, as well as people here will help you, but you have to decide what you want to do and how far in you want to get. There are kits out there you can buy even whole modules that may do what you want.

Where are you located as unless it's on the far side of the moon almost all IC's should be available to you if not someone difficult to obtain.

 

[magester1]

I am interested in all this, and willing to get deep into it. I'm used to programming with C, mainly C++, and know the basics of Basic.
My problem is exactly that: location. Right now, and untill March, I'm in a city where I can buy resistors at most. And shipping ICs from somewhere else would be too expensive for this. I once wanted to purchase the classic 555 to try it out when I started reading about electronics, and was told that they didn't have any kind of ICs here, not even that one.
I do have some digital ones salvaged from computers and other electronic equipments, and other common ones like op-amps. But I'm sure it's unlikely for them to be of any use if I need specific ones.

I'm guessing from all this that I'm trying something a bit too complex at the moment. Is that right?

Anyway, thanks for all your help.

By the way, which kind of ICs would I need for this?
I'll leave micro controllers out for now.

 

[Sceadwian]

and know the basics of Basic

I got a chuckle from that if it wasn't intended as a joke it was amusing anyways =)
What city do you live in where you can get discrete components and no IC's? That doesn't make sense. They can't have discrete and not have 555s or more complex ICs.

Micro controllers aren't inherently complex, I think they should be better described as involved. Many micro controllers can be cheaper than more involved IC's.
Name your location or I can't suggest anything.
For overall functionality complexity and availability a micro controller would actually be easier than discretes and other ICs. Simply because a single micro controller can replace hundreds if not thousands or discrete ICs.

 

[magester1]

"The basics of Basic" is what I always say, xP. It's more fun that way.

I didn't mention the city since I don't think you'd know it. I'm from Argentina, live in the capital of it. Right now I'm in a small touristic city called Bariloche, far from main cities.
I always wondered the same thing, how come they don't sell ICs?!
What's more, they used to sell them. I renember when I was a kid my father bought me one of those kits which bring a PCB, components and everything, all you had to do was put it together and solder it. Now, when I went there to ask, I was told they could supply me only with the resistors and such but not the ICs. I'll go ask again tomorrow, since last time I did was more than half a year ago.

Micro controllers are indeed the best choice, since I could use them for a lot of other things too, being myself more familiar with coding programs than designing circuits. But I'd have to purchase a Programmer, and if I can't get a 555, I certainly won't get a PIC, let alone one of this. Unless making one myself is an option.

 

[Sceadwian]

Where is 'there' that you asked for this information from?

I'm absolutely positive that you have some shipping possibilities that won't kill your pocket book for ordering IC's and programmers, especially considering some very basic PIC and AVR (micro controller chips made my Microchip and Atmel respectivly) can be made using only a few discrete transistors resistors and capacitors. There is a wealth of information available out there. Start a new thread specifically about suppliers to where you're located hopefully there are a few other people on the forums that can help you. Try updating the thread every few days if no one responds and keep looking on your own, eventually you will be able to find a solution to get reasonably priced parts without excessive cost.


Definitely your A1 single most important thing to do is read everything you can find about what you're interested in, and find a supplier for parts that won't break your bank account. Everyone here welcomes questions, the only thing we ask is to try to do your own research first, come here with what you've found and usually someone will be able to aim you in the right direction.

Being in a moderately sized US city I'm kind of spoiled, there's almost nothing I can't get with a few mouse clicks on a web site mailed within 48 hours and at my door within a week

 

[magester1]

I will search and see what I can get. Besides, you are right, this isn't the place to discuss this since I started the thread for something completely different.
Where I asked for the components is a local "electronics" store. They don't even have a website.
I'll try getting micro controllers then. Will make most things easier.

Anyway, thanks for all your help.
I appreciate you taking the time to answer all my questions.

 

[magester1]

I didn't really think I was going to write back in this post. However, after some research I've decided for the microcontroller solution. Way easier and I can use it for anything I want.
So, I wrote a program to interpret the 1ms-2ms signal and convert it into a 0-100% Duty Cycle PWM and unless my code was wrong the signal is actually shorter than that, maybe 1-1.8ms.

Anyway, that worked fine, but I'm still having some issues. Which brings me to my question in this very same post. Whenever I get the Radio Control near the receiver it simply stops working, after some testing with code and LEDs I think the problem is that it just reads more than 2ms regardless of the channel position. It also varies with the length of the antenna: full length means I've got to be even further.
What I'm not sure though, is if it's a problem with the receiver or maybe interference with the PIC (using the 16F628A by the way). Is that possible?

I hope it's OK to ask in this same post.
Thanks for reading.