Strange values from 2ch receiver

Hello,

I've followed this tutorial:
https://www.sparkfun.com/tutorials/348

it works. I've used a 27MHz 2Ch Receiver and transmitter. But if the rc transmitter is turned off, the values of [ch2 = pulseIn(7, HIGH, 25000); ] gets strange.

Channel 2: 346
Channel 2: -29
Channel 2: -528
Channel 2: 316
Channel 2: -125
Channel 2: -700
Channel 2: -17
Channel 2: -377
Channel 2: -700
Channel 2: 562
Channel 2: -42
Channel 2: -700
Channel 2: 5
Channel 2: 1776
Channel 2: -71
Channel 2: -428
Channel 2: 1279
Channel 2: 144
Channel 2: 521

Where are the values coming from? The values should be always 0 when the transmitter is turned off.

Power on the transmitter and I get normal values:

Channel 2: -5
Channel 2: -3
Channel 2: -6
Channel 2: -5
Channel 2: -4
Channel 2: -6
Channel 2: -6
Channel 2: -3
Channel 2: -6
Channel 2: -6
Channel 2: -5
Channel 2: -5
Channel 2: -8
Channel 2: -9
Channel 2: -7
Channel 2: -8
Channel 2: -7
Channel 2: -7

I also tried to use pullup-resistor [ digitalWrite(7, HIGH); ]
but it doesn't help.

And I have not many knowledge in electronic. Someone can help me?

Is AGC enabled in the receiver?

AWOL:
Is AGC enabled in the receiver?

i have no idea how to find the AGC in the receiver?

The receiver is looking like this http://www.tamiyaclub.com/tc_userimages/169/img169_LYD9A_2.jpg
but RX Band 6

ive opened it, but couldnt find jumpers or switch

I found out that these interruptions came from usb from PC.
Plug off USB and plug in battery to arduino-> no more interruptions.

But I dont want plug off USB from my PC - so how can I eliminate these interruptions?

I have run into these problems time after time when running Arduino off external power. What you should do is to add some capacitors across 5v and GND. It's generally a good idea to do this with any power supply to eliminate noise. If you are using the Arduino to regulate it's own voltage, put caps between vin -> GND, and +5 -> GND.

EDIT:
Also are you doing anything else with your Arduino? What I mean is when your are reading the values is anything else happening or drawing power?

I want to use this values to drive 50A H-bridge motors

okay, which type and which value of capacitor should I use?
Electrolytic 47nF or ceramic 100uF ?

I have to learn using correct caps

When the transmitter is off, the receiver is outputting noise. It's the nature of the system. Since this is 27Mhz AM system, it must be very old (~20 years). If you want a reliable output from the receiver when the transmitter is off, you need a more modern system.

I've tried 100nF capacitor and then tried 100uF but it doesnt help.

@afremont:

but there are no noise if I use battery instead of usb power.

Which is the cheapest modern system and easy to use?

I have used modern AM 27mhz receivers and typically when the transmitter is off, the the receiver outputted little noise. Cheap rc cars and planes ship with these am radios still. They are not uncommon. Try seeing what the arduino reads if there is absolutely nothing else drawing power from the system. Also, some code would help.

forgoden:
I've tried 100nF capacitor and then tried 100uF but it doesnt help.

@afremont:

but there are no noise if I use battery instead of usb power.

Which is the cheapest modern system and easy to use?

I haven't flown model planes for about 20 years and even then, AM was not being sold any more. I really wouldn't know what to tell you, but a quick look at some RC hobby site should make it clear. My old system is FM operating at 49MHz and was being replaced at the time with an FM/PCM system of some sort. I would suspect that anything you buy, even the cheapest system will give you better performance and will be operating on higher frequencies. It will also likely be much easier on the batteries.

You are fortunate that your system is showing its weakness to EMI or RFI noise now instead of later when it causes a problem. The reason that AM was replaced was that it was very susceptible to interference of all types which results in lost/crashed planes.

This may be a good choice:
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8338
I'm not very sure what kind of transmitter you are looking for.

Wow, I didn’t think you could still get a transmitter that didn’t have an LCD display. Cheap as that is, it will probably be more dependable. I know there are receivers (and have been for some time) that will output fail-safe pulses when the transmitter is not being received.