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Neptune769

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Hello Everyone,

I am new to this forum and see there is plenty of knowledgeable people here. First let me say I don't know much about electronics or PICs & AVRs or programing. I do know how to read schematics and I can assemble kits and make boards. Now here is my project. I am building a ROV for underwater. I need to be able to use a RC transmitter less RF module. The end result is that I need proportional control of three motors with electroinic speed controls. That is on one stick and a trim pot third channel for the third motor. Then on the other stick pan & tilt camera control. Then from the TX over RS232 I need to control zoom with trim pot, Manual focus (up & down push buttons), Iris (up & down push buttons), Shutter speed would be nice but not necessary. I have the camera control commands. I was going to use a http://www.futurlec.com/ATMEGA8535_Controller.shtml and a http://www.pololu.com/catalog/product/207 for the Speed control portion as well as two on off switches for lights & pan/tilt servo. My problem is that I don't know how to get the TX encoder to communicate to the AVR. Then I would need someone to do the programing. I have someone that is willing to write the program for the camera controls. BTW the camera is a Hitachi VK-S234. I can't find a data sheet on this camera but the VK-S274R and VK-S914. Attached is the data sheet. I tried to attach the control command PDF but it is 1.3MB. Let me know what you all think. Any input would be appreciated.

Regards,

Dennis

VKK274R.pdf

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Pretty ambitious project. For the control of everything, if you aren't looking for an RC system, look into the xbee modules. I believe that sparkfun sells them with analog inputs, so you could use pots directly into the xbee. You'd have to double check, it's been a while since I looked at them. You could send serial commands directly into the module and have them come out of the mobile unit and go directly to the camera.

For speed controls of three motors, what kind of motors are they? You may just want to use actual speed controllers and just send them the appropriate signal rather than trying to do your own thing there.

You should look into the xbee modules, they will probably allow for most of what you want.

Your main issue will be the RF through water. Make sure the transmitter antenna is underwater also, as you will lose a lot of signal when the it refracts against the surface of the water if it is above the water.

What kind of raneg are you trying to accomplish with this thing?

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You should look into the xbee modules, they will probably allow for most of what you want.

Your main issue will be the RF through water. Make sure the transmitter antenna is underwater also, as you will lose a lot of signal when the it refracts against the surface of the water if it is above the water.

In his other post he detailed a bit more that he wanted to go wired, not wireless for that reason.

Regarding the speed controls, it would be easy to take common R/C car controllers and go wired by hacking a cheap PPM receiver to accept the transmitter's PPM signal without the RF parts.

But the RS232 part is a tad more tricky, i'd make the interface module so that it accepts individual servo signals as inputs, and would connect it to the other outputs of the receiver in the vehicle.

So, R/C TX's PPM output sent onto the cable, signal fed to the decoding part of a receiver onboard the vehicle (bypassing the RF circuitry), then 3 car speed controllers plus camera interface module connected to the receiver outputs.

It would be wise to follow the technique Thomas mentioned in the other thread to send the power and data over the long cable, or at least amplify the signal on the TX side and restore it to appropriate levels on the RX side.

Edited by Kilrah

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Just a thought but, why not send the RF down a coax cable to the bottom as well as the DC with the appropriate blocking capacitors to operate the electronics and use a receiver at the bottom hooked up normally to decode the RF and operate the servos. There would be enough RF at the end of a 100 or so feet of cable with just a stub antenna to accomplish this. In fact, may have to attenuate the RF somewhat...

Only modification would be to the transmitter which would mean putting a coax connector instead of an antenna on the transmitter.

Edited by W3FJW-Ron

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In his other post he detailed a bit more that he wanted to go wired, not wireless for that reason.

Regarding the speed controls, it would be easy to take common R/C car controllers and go wired by hacking a cheap PPM receiver to accept the transmitter's PPM signal without the RF parts.

But the RS232 part is a tad more tricky, i'd make the interface module so that it accepts individual servo signals as inputs, and would connect it to the other outputs of the receiver in the vehicle.

So, R/C TX's PPM output sent onto the cable, signal fed to the decoding part of a receiver onboard the vehicle (bypassing the RF circuitry), then 3 car speed controllers plus camera interface module connected to the receiver outputs.

It would be wise to follow the technique Thomas mentioned in the other thread to send the power and data over the long cable, or at least amplify the signal on the TX side and restore it to appropriate levels on the RX side.

Hi Kilrah,

The serial isn't as much of a problem as is it to bypass the RF circuit. I wouldn't know where to start. I have been trying to figure out a way to replace the TX RF module with a microcontroller that has analog inputs and can output RS232. I have an old Futaba FG series TX that I want to use. I found a data sheet for the encoder IC. I would like to rind a schematic or service manual on this radio. Or at least the pinout for the 5 pin RF module plug. I'll try to find the thread you mentioned.

Thanks,

Dennis

Dennis

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Just a thought but, why not send the RF down a coax cable to the bottom as well as the DC with the appropriate blocking capacitors to operate the electronics and use a receiver at the bottom hooked up normally to decode the RF and operate the servos. There would be enough RF at the end of a 100 or so feet of cable with just a stub antenna to accomplish this. In fact, may have to attenuate the RF somewhat...

Only modification would be to the transmitter which would mean putting a coax connector instead of an antenna on the transmitter.

Hi Ron,

My reasoning for eliminating the RF is because the TX & RX is pre 1991 and I don't want stray RF flying around. Granted I don't think the RF Police (FCC) would know. And I don't want to have the radio updated. I could go and buy an updated RC set but that would add more than I would like to the budget. Also the plan was to gut the TX and build everything into a Pelican case with monitor in the lid for the video. The plan is also to go about 300 feet. I do appreciate the info though I will keep it in mind. I will take all ideas into consideration since I really don't know what I'm doing. The electronics portion of this project is a huge learning experience. :) Thank to all the forums I'm on and all the great people on them I am getting allot of info and help.

Regards,

Dennis

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New Transmitters can be found for between $50 and $100 so that part would not be a problem for you and it doesn't make any difference how old the receiver would be as long as it's reliable in operation. & I wouldn't worry to much about RF as we're only talking about 2, 3 microvolts in the ROV. Just enough to operate the receiver. Oh well, 'nuff 'o that.

There are plenty of receiver decoder chips available that will split a ppm signal into servo channels with a few additional parts.. That may be all you need.

BTW, I spent about 3 1/2 hours on the Pololu site last night. Real interesting stuff. You might consider using a small laptop with a USB to RS232 dongle & use the laptop as the controller as well as the monitor and control one of their 8 or 16 servo controller boards.. Might not be too hard to learn the C+ stuff with their program if it's a drag & drop GUI program. I downloaded it but I'm like you. No programming knowlege to speak of. Might just have to buy one of their PIC programmers for $59 though....

This topic is turning into a passable "Think Tank" topic though. I'm learning as well as you...

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The serial isn't as much of a problem as is it to bypass the RF circuit. I wouldn't know where to start.

If you have access to an oscilloscope it's a matter of minutes, if not it's just a few more minutes :)

With a scope you'd just probe the RF module port or the trainer port if the radio has one looking for a PPM signal that looks like this:

ppm.jpg

Without one, either look at the encoder's datasheet and find the output, or simply follow the PCB trace that goes from it to the RF module...

Once you find that signal you have what you need to send down the cable.

On the receiver side, most older /simple and cheap PPM receivers use a 4017 decoder. Inputs are either pin 13 or 14 from the datasheet depending on the polarity of the signal. The idea is to cut the trace that is between the RF part and the decoder and inject your signal there. A scope would help as you need to cut at the right place to keep the reset circuitry active (it reacts to the long low time you see on the diagram above after the last servo pulse to reset the decoder to the first channel). With no scope you could have a look at the RF demodulator IC's datasheet, find it's output and you'd be quite good about the place to inject the signal to. Maybe some signal reforming would be needed, but you'd be very close.

Edited by Kilrah

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If you have access to an oscilloscope it's a matter of minutes, if not it's just a few more minutes :)

With a scope you'd just probe the RF module port or the trainer port if the radio has one looking for a PPM signal that looks like this:

ppm.jpg

Without one, either look at the encoder's datasheet and find the output, or simply follow the PCB trace that goes from it to the RF module...

Once you find that signal you have what you need to send down the cable.

On the receiver side, most older /simple and cheap PPM receivers use a 4017 decoder. Inputs are either pin 13 or 14 from the datasheet depending on the polarity of the signal. The idea is to cut the trace that is between the RF part and the decoder and inject your signal there. A scope would help as you need to cut at the right place to keep the reset circuitry active (it reacts to the long low time you see on the diagram above after the last servo pulse to reset the decoder to the first channel). With no scope you could have a look at the RF demodulator IC's datasheet, find it's output and you'd be quite good about the place to inject the signal to. Maybe some signal reforming would be needed, but you'd be very close.

Hey that will work. I think it is time to get my dad and his scope involved. :D Thanks for the info.

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