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Feb 25, 2008, 02:50 PM
Impossible? Hah!
KreAture's Avatar
Hmm. Maby not a bad idea.
So, if a RX is powered up it will wait at a specified channel for it's TX to give it a new one. Regardless of channel-hopping. Missing acks would mean rebooted TX, out of range or distrubances. Hmm.
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Feb 25, 2008, 03:16 PM
Registered User
KreAture , my hopping sequence is a psuedo random permutation of all the channels available. The random number generator is seeded by the mac address of the rx. This way the rx only needs to know the current sequence index to syncronise. The hopping is at a fixed time interval so it does not matter if a packet is missed, the rx uses its clock and the known sequence to know the channel to use. A sort of software pll is used to keep the clocks in sync.
Feb 25, 2008, 04:30 PM
Impossible? Hah!
KreAture's Avatar
Ahh. The nRF doesn't use 802 or any such codec. It uses small manageable packets of up to 32 bytes whereof up to 40 bit can be the address and 8 or 16 bit can be the CRC. CRC is generated by the nRF chip automatically.
Since I use 16 bit CRC and address I then have 28 bytes of data capacity pr 32 byte packet giving a 4 byte overhead. It looks like sending at 250 kbps will be best for range so I will do that. Alternatively I could send at 1Mbps.

I am unsure how I will do the actual channel hopping myself. I have a backup RF channel I will use to send commands for hopping though, if the main channel is not getting though. The 200Ás switching time should make it possible to switch and confirm fast.
Feb 26, 2008, 01:31 PM
Registered User

Are you sending 12 separate PWM signals directly into the module, or are they combined like a PPM signal, or a serial data stream? It sounds like you are sending it 12 separate signals.

I'd love to see the Jennic modules put together in a full range system like these guys have done with the Xbee: (in French).

Feb 26, 2008, 02:14 PM
Registered User
Jeff, The data for all channels is sent in a single serial packet, the packet can hold just over 100 bytes so over 50 16 bit channels could be sent in one packet. I am planning to send the primary 4 or 8 channels in every packet and any further channels far less often using the following rules-
1. send every .5 sec to allow for the case of the rx rebooting
2. send if the there is a change in input so latency will be low
3. send if not ack'd
This allows for a virtually limitless number of auxillary channels without excessive use of bandwidth.

ps I have 21 not 12 servo outputs, it was hard work so I care
Feb 26, 2008, 06:58 PM
Registered User
I just started drawing stuff up and thought I'd start with the basic circuits that I have been using for testing. As you see there is not a lot to it.

tx - the a/d measure between 0->2.4v so you might need an extra resistor in series with the +ve side of the pot.

Ignore the regulator part number, it was just the first one I found in Eagle.

The modules come with a bootloader installed.
To program the module, connect TXD0 & RXD0 to a pc through a logic level serial port. To enter programming mode hold the spimiso low as you power up the module and then release it.

Mar 02, 2008, 05:14 PM
Holger Rusch
Prof. Dr. YoMan's Avatar
Any news?

Advanced hopping? Hopping speed?

More tricks?

Changeing of the "gold" codes possible?
Mar 03, 2008, 03:44 PM
Registered User
Prof. Dr. YoMan, nothing much to report. I am working on some pcb layouts so that I have something robust to start getting some flying hours/testing in.

Can anyone recommend a cheap/available low drop out 3.3v 200ma ish regulator for the receiver that will cope with both a single lipo and a fully charged 6v nicad pack?

Mar 04, 2008, 12:32 PM
AndyKunz's Avatar
There's a part in the LT1121 family that should do the trick for you. I forget the p/n offhand but it's only a single digit different.

Mar 04, 2008, 12:40 PM
Here is a 240mA part for <$1:

Regulator Type: Single Output
Current: 240mA
Voltage 3.3V
Package / Case: SOT-23L
Mar 06, 2008, 03:57 PM
Registered User
Andy,rmteo, thanks for your suggestions, they are much appriciated. As the regulator is the only significant component for the rx, other than the rf module, I thought I'd spend some time getting it right, I found myself drowning in a sea of datasheets.

For the mk1 rx I am going for as many outputs as fit the width of the module ( 5 or 6 ) and am planning to gang the analog inputs with the outputs so that software can select between servo output or analog in. I shall also use the I2C lines for two of the outputs, so two servos could be sacrificed for whatever I2C stuff comes to mind.

Has anyone else tried these modules yet? If so I will happily share my code with you, it just hasn't yet stayed still long enough to publish.

Mar 06, 2008, 04:27 PM
Registered User
I cant wait to see the final results and build one of these systems. I have my PS2 controller waiting to be torn apart. I dont have a regular TX so this will be fun to start from scratch especially if it is working with 4 channels. DIY is always more fun than buying.
Mar 06, 2008, 05:32 PM
Registered User
crazifunguy, here is a picture and the circuit of my current ps2 setup, as you see it should be no problem fitting it all inside the controller. I have 4 channels of trim on the buttons near the joysticks. My plan is to select auxillary channels and functions with the left two fire buttons and set their value with the right two. I have flown with this a few times and found it hard to be subtle with the short joysticks.

Mar 06, 2008, 10:26 PM
Registered User
My name is Bob Kreutzer and I hope you might be able
to help me with my skateboard project. I am currently using a standard HiTech 2 channel land based R/C
unit to controll my electric skateboard. I am using a Jetti
JES80 amp controller on a 450 watt motor .

I am looking for a transmitter and receiver unit that
I can program the acceleration and braking curves
to this brushed motor.

Can this unit that you are experimenting with be configured to do such a thing?

( I have pictures of my project if you care to see them )


Bob K
Mar 08, 2008, 12:20 PM
Registered User
Bob, there should be no problem doing what you want with these modules as long as you are happy programming in C.

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