IBC radio problems
well folks its that time again.
I have gotten off my ass and have some news for youse.
As some of you may know plan-B lost on the second day primarily because of radio trouble (nothing to do with our compeditors or nothin).
Anyway I have been moving on making a 2.4 Ghz 2 way digital radio setup so we can do our own plan of funkyness on it.
now whilst i have the hardware for that wired up there is still some bug fixing to do before it works.
Now for the interesting part...
because it dosent look like we will get the new digital radio going for marryong 7 we started looking at ways to get better signal with our existing radio. To that end we are putting in a base loaded top hat (capacity hat) antenna. Now we were just looking for a proof of concept so we wired it up and i did a range test inside our house (tx antenna down).
We got about 30 meters range... before i ran out of house.
This is how it was set up.
Note the extensive use of the TLAR principle (that looks about right) in the antenna design and coil construction. Point is it worked and more than well enough for robot wars.
now heres were it really gets interesting
we put the reciever and antenna in the bot (no changes) powered the bot up and promptly found our radio range (as judjed by IBC and servo) was around 2 meters. After much fiddling and tuning we got about a 10% signal at 4-6 meters with perfect tx and rx antenna (tx extended, and rx out of the bot and nicley presented)
now heres where it really really gets interesting
i had a bit of a brain wave, left everything where it was, radio, bot etc, just unplugged the ibc and plugged the rx battery back in. range went up to about 8 meters ( at 10%). then it got interesting. we switched the bot off. range went back up to the point we didnt have enough land to get the servo to twitch noticablly with the antenna down. Worst we got was a slight vibration when i had the antenna down the radio on the ground and pointing horisontally away from the reciever. Then we switched the bot on, servo went spastic for a second then died.
radio range was about 3 meters with tx down.
Now keep in mind that the radio and bot *were not connected* by moving the radio away from the bot radio range went up.
Now for some less interesting stuff, unless your an electronics nerd in which case its probbly hella frustrating. feel free to skip to the conclusions.
heres a bad photo of my scope
This is taken from ground to the *antenna* ie this should be basically only be seeing random low level noise, instead we have a .1V signal blasting across the spectrum *and* this is after encasing the IBC in a grounded foil sleve.
it seems to have 3 or more frequency components and 4 distinct stages
the 2 pulses are 4 usec apart
the high freq noise has a period of .125 usec and there is another signal at about .8 of a volt that i cant clearly determine the frequency of but it isnt much higher.
quick quackulation
the high frequency noise is at 8 mhz, this is pretty damn close to what is mixed with the input freq to make the IF(intermediate frequency) (in our case the radio has an 11 mhz xtal in it so some of those higher freqs may be almost directly on this mixing freq)
the AVR runs off a 12 mhz xtal so that shouldnt be it.
the pulses are spaced at .25 mhz and occur at about .1mhz so i dont think they will be doing anything much.
also we noticed that the input line from the rx sits high but gets pulled low at 1Hz
Conclusions
The IBC is spewing RF noise like a football team after a bad curry and 2 hours on a dirt road.
possible solutions.
a thick grounded AL box may help to attenuate the RF being spewed out.
run the reciever off a battery.
opto isolate the RX from the IBC and keep the IBC leads inside the box.
we are just about to test the IBC battery connections and motor leads for noise.
hopefully this is mainly confined to the logic side of the board.
(personally i'm pointing my finger at either the SEPIC converter (possibly) or perhaps more likley the HIP chip's charge pumps.)
P.S
just did some more testing
without motors connected and radio off we saw simmilar noise with the pulses and hf at the same freqs coming out the motor lines, there was a small <0.01V of that signal on the battery lines.
i'm thinking its probbly the charge pump in the HIP chips more now
i'll do some more playing later and see what i come up with
I have gotten off my ass and have some news for youse.
As some of you may know plan-B lost on the second day primarily because of radio trouble (nothing to do with our compeditors or nothin).
Anyway I have been moving on making a 2.4 Ghz 2 way digital radio setup so we can do our own plan of funkyness on it.
now whilst i have the hardware for that wired up there is still some bug fixing to do before it works.
Now for the interesting part...
because it dosent look like we will get the new digital radio going for marryong 7 we started looking at ways to get better signal with our existing radio. To that end we are putting in a base loaded top hat (capacity hat) antenna. Now we were just looking for a proof of concept so we wired it up and i did a range test inside our house (tx antenna down).
We got about 30 meters range... before i ran out of house.
This is how it was set up.
Note the extensive use of the TLAR principle (that looks about right) in the antenna design and coil construction. Point is it worked and more than well enough for robot wars.
now heres were it really gets interesting
we put the reciever and antenna in the bot (no changes) powered the bot up and promptly found our radio range (as judjed by IBC and servo) was around 2 meters. After much fiddling and tuning we got about a 10% signal at 4-6 meters with perfect tx and rx antenna (tx extended, and rx out of the bot and nicley presented)
now heres where it really really gets interesting
i had a bit of a brain wave, left everything where it was, radio, bot etc, just unplugged the ibc and plugged the rx battery back in. range went up to about 8 meters ( at 10%). then it got interesting. we switched the bot off. range went back up to the point we didnt have enough land to get the servo to twitch noticablly with the antenna down. Worst we got was a slight vibration when i had the antenna down the radio on the ground and pointing horisontally away from the reciever. Then we switched the bot on, servo went spastic for a second then died.
radio range was about 3 meters with tx down.
Now keep in mind that the radio and bot *were not connected* by moving the radio away from the bot radio range went up.
Now for some less interesting stuff, unless your an electronics nerd in which case its probbly hella frustrating. feel free to skip to the conclusions.
heres a bad photo of my scope
This is taken from ground to the *antenna* ie this should be basically only be seeing random low level noise, instead we have a .1V signal blasting across the spectrum *and* this is after encasing the IBC in a grounded foil sleve.
it seems to have 3 or more frequency components and 4 distinct stages
the 2 pulses are 4 usec apart
the high freq noise has a period of .125 usec and there is another signal at about .8 of a volt that i cant clearly determine the frequency of but it isnt much higher.
quick quackulation
the high frequency noise is at 8 mhz, this is pretty damn close to what is mixed with the input freq to make the IF(intermediate frequency) (in our case the radio has an 11 mhz xtal in it so some of those higher freqs may be almost directly on this mixing freq)
the AVR runs off a 12 mhz xtal so that shouldnt be it.
the pulses are spaced at .25 mhz and occur at about .1mhz so i dont think they will be doing anything much.
also we noticed that the input line from the rx sits high but gets pulled low at 1Hz
Conclusions
The IBC is spewing RF noise like a football team after a bad curry and 2 hours on a dirt road.
possible solutions.
a thick grounded AL box may help to attenuate the RF being spewed out.
run the reciever off a battery.
opto isolate the RX from the IBC and keep the IBC leads inside the box.
we are just about to test the IBC battery connections and motor leads for noise.
hopefully this is mainly confined to the logic side of the board.
(personally i'm pointing my finger at either the SEPIC converter (possibly) or perhaps more likley the HIP chip's charge pumps.)
P.S
just did some more testing
without motors connected and radio off we saw simmilar noise with the pulses and hf at the same freqs coming out the motor lines, there was a small <0.01V of that signal on the battery lines.
i'm thinking its probbly the charge pump in the HIP chips more now
i'll do some more playing later and see what i come up with
posted by Valen at 7:19 PM
0 Comments:
Post a Comment
<< Home