FrSky Modules - Is this a problem??

[GBR2]

Over in the FrSky thread on RCGroups Radio forum, it was recently brought up that it appears the PPM signal of most transmitters is at a higher voltage level than the specification for the IC receiving this signal in the FrSky modules. It appears that this IC has some diode protection with a current capacity of 2ma, per that thread. Various circuits and voltage divider schemes have been posted in that thread with the goal of protecting the IC from being damaged and possibly causing the module to die. I believe FrSky posted not only a circuit that could be used but were going to incorporate it in all future manufactured modules. So the question is, how safe are all the modules that are currently out in the world??

I've got both a non-telemetry and telemetry module, both of which have this "issue". I've flown with the non-telemetry module in a glider for a while now with no issues using a JR XP9303 but now I'm wondering how safe is this to do??? A destroyed model I can live with but possible collateral damage, such as hitting someone, is another ball of wax. For me, I'm grounding FrSky till I can get some sort of assurance that this really isn't an issue but is sure sounds like it is.

[crampy]

Hmmm, I'll be keeping an eye on this. I've also got an older non-telemetry module in my Turnigy 9X.

[RCModelReviews]

I'm not that familiar with the maximum ratings of the Atmel processors but I know that PICs (another family of microcontroller) can handle up to 20mA through its clamping circuitry on any input. (I just checked and it looks as if the Atmel processors also have a 20mA sink capability -- although that's not specifically stated as their over-voltage sink capabilities on an input).

I'll take a look at the circuitry of the DIY module but I'm thinking that so long as the PPM signal is 5V p-p and has a series-resistance of at least 85 ohms then it's operating within the specs of the chip.

[RCModelReviews]

I see that FrSky have announced they'll be updating their DIY modules to ensure no problems occur due to a potential overdriving of the input and that they'll be providing dealers with the parts needed to retrofit any existing installations.

That's a pretty good response, especially for a Chinese company. I don't recall Corona or any other Sino-RC company doing this much to rectify a potential problem.

[crampy]

So, are these parts being offered for free from our supplier, or do we need to pay for the fix?

[GBR2]

Here is a posting from FrSky over in the RCGroups thread:

For those module-based transmitters, their PPM output should be high-inpendence, so we don't think overdrive needs to be concerned. (In fact, Futaba, JR modules are the same with ours. When using V8FT, V8JT, DFT and DJT with transmitters listed on our instruction manuals, no need to concern about overdrive issue.)

As for V8HT and DHT(two way telemetry DIY hack module which would be coming out soon), here are our replies:
Firstly, we will take Phil_g's propose into our following batchs of V8HT (for detailed information, please kindly find in post #1203 of this thread), and put different bar code onto these modules to distingush with former ones; as for DHT, we have already added this new circuit.

Secondly, for V8HT in-our-stock, we will add the diode to make sure the input current safe and make notice in instruction manual;

Thirdly, for those modules which have been sold out, we will provide our dealers/distributors wires with diode on for users to add to their modules; meanwhile, we will make announcement on our website too to keep users updated and noticed.



Thank you all for your attention.
Best regards!
Eva
********************8
That makes me feel a whole lot better about my module and I'll be putting it back into service. As to my Telemetry module, I'll get a BAT85 from work and install it in the Telemetry module. Nice to see such a fairly quick response from a company for a change.

[crash]

I guess I better contact extreme RC to send me the diode and instructions where to fit in my Hack module II fitted to my MC 24?

Then he has my address details so maybe he will send it to me anyway?

Chris?