Mode Zero

Here we go! First in the list of ‘conversions’ this lovely OS Cougar is to have a Digispark 4 channel encoder and a JR 35mhz RF.
The Digispark has very recently been received from Phil Green.

It’s a step up from my Ladybird book of Magnets Bulbs and Batteries. So I’m going to need a little help here as I’m not sure it’s working correctly?

So far the RF stage us belting out a signal. The throttle buzzes if the stick is in the wrong position on switch on but I must have it wired back to front as it squeals when it’s down not up. Easy fix me thinks.

Followed the press to break micro switch routine to calibrate the sticks. Got a green LED light on the Digispark But so far no movement on my servos.

Early days but any thoughts much appreciated

Morning musings suggests I need to check for PPM - if not present or not getting to the RF it would produce the results I’m getting

Hi,
Re. calibration: did you remember to press and hold the button before/while you power up the Tx / Digispark?

Hi Jonathan

I might be wrong, but I seem to remember that JR 35MHz modules are quite fussy about the PPM signal they require, they require the polarity that is predominantly positive and just the short separation pulses going to 0V (though I think Phil prefers to call this negative polarity) and this short separation pulse is 400uS, not 300uS like is used by most of Phil's encoders. It's worth PM Phil to check as he knows more about this than me.

If you haven't got a PPM tester, it's well worth building one and there are a couple on the forum by Phil and Ceptimus. They save having to get the logic analyzer or scope out and are worth their weight in gold for these types of conversions.

Cheers Mike

Hello Mike well my brain was working this eve. Used a small audio amp to probe the PPM and it proved it was present . Then tried a Futaba RF board with same crystal. Same result - belter of a signal but nothing at the rx . Then became suspect of tx crystal. Changed it and works perfectly! So that tx crystal is way off frequency . Going to put the JR RF stage back now .

Well done Jonathan and Mike...some good ol Norfolk and Good (!) fault finding, seems we have to do a lot of that in these here parts?!?!

I always thought that JR and Futaba transmitter crystals on 35MHz weren't interchangeable, though I don't remember ever testing it out. I often used one make of transmitter with the other make of receiver - worked fine for non-PCM with both single and double conversion receivers, but I always used Brand X crystals in Brand X equipment - whether that equipment was a transmitter or receiver.

I think some transmitter crystals actually resonated at half or quarter the transmitting frequency, and the numbers stamped on them were the transmitting frequency - not the actual crystal frequency. But I don't remember if that was a JR or Futaba thing. Phil will likely know.

Not sure about JR but Futaba double from a 17.5mhz fundamental and Hitecs triple from 11.6mhz so the two are not interchangeable. Never had a JR
If you need a neat, compact 35mhz RF module tbe Hitecs and Jamaras are hard to beat, and cheap!
viewtopic.php?f=62&t=706
viewtopic.php?f=24&t=137&p=4081&hilit=Jamara#p3699
Cheers
Phil

I did a lot of conversions to 35Mhz using mostly Futaba and Jamara modules, but some JR ones also.
Most of JR (in Germany Graupner) modules require the PPM signal to be reversed, but not all of them, there are some exceptions.
Futaba and Jamara crystals are interchangeable, but not JR ones. A JR crystal will not work in a Futaba module and vice versa.
Some of the JR modules (not all) require a separate regulated 6V DC input in addition to the 9.6V input and the PPM input.
So JR modules require a little more effort for conversions.

Frank

Thank you guys I have read your contributions with much interest. One of the links took me to Franks replica single channel transmitters. Absolutely blown away!! I have also looked up Jamara modules.They seem to be very expensive at £60 each. However there seem to be plenty of Futaba modules on eBay Under a tenner. However I have bought a few completely trashed Futaba challengers in the past for similar money. With the added benefit of being able to salvage switches et cetera. I’m really pleased I’ve got everything working now. The next stage is to clean up the interior of the transmitter and work out where I’m going to put all the bits. Now that shouldn’t be difficult now all the working parts are tiny! Really enjoying this forum thank you all for your contribution