First step is to determine what voltage the Dynon is using for the RS232 communication. That will tell you what sort of devices it is compatible with and whether you will need some form of voltage control. The RS232 standard allows for a very large voltage range, but not all devices can cope with the full range.
Its a Dynon Skyview 7 inch display the display has 5 serial inputs that can be utilized for a range of accessories, GPS, Nav, Radio, Transponders ect ect.
All i can find in the manuals and all other searches is that the serial ports utilize RS 232 and that’s it no other specs.
In regards to me fiddling with it, its my families aircraft and in an experimental category so “uncertified” equipment. This GPS receiver I am trying to integrate in this application is only used as position fix to aid calibration and accuracy of the compass (Not required but helps). The the primary nav is through another independent device. Thought id have a go as a bit of fun and also save a few hundred bucks on the genuine Dynon receiver.
RS232 has it’s “own” specs which used to be adhered to but over the years has got a bit out of hand. So much so that one piece of equipment may work with equipment X but there is not much guarantee it will work with equipment Y. Having said that though I think manufacturers have made their equipment much more flexible and might work with 5V and ground while still able to withstand a “proper” RS232 of +/- 12V. I don’t know about this as I have been retired for a number of years now and have not kept up with all the details of any changes. I may have rose coloured glasses on but if I purchased a piece of “RS232” equipment I would expect it to work with any level from the bottom end of the scale through to the upper limit. I might be dreaming too.
Measuring the signal levels. Ideally done with an oscilloscope if you have access to one. While any signal is bouncing around a DMM or analog meter could read anything. I have a feeling though that RS232 will come to rest at a HIGH condition with no traffic. This had to be, as from memory some low power devices were actually powered with the signal voltage. Long time ago now.
I raised the subject of aircraft as back in the early 70’s the company I worked for had operations in PNG. While in Lae we shared a workshop with our Aviation division. Our division (engineering products/marine) and Aviation had a common customer. SDA Mission who had their own aircraft operation and also operated a HF SSB network. They wanted to fit SSB transceivers to their aircraft (workhorse Cessnas). Not too big a problem technically as all the aviation techs were licensed and we could set up the actual radio unit but I believe this created a mountain of documentation. Weight and power requirement of the actual radio, position in the aircraft had to be documented and the list goes on. The rules have probably changed radically over the years and the difference between that scenario and yourself is that was a commercial operation and often carried passengers. Not in a commercial sense but for SDA operations.
Very interesting project and I wish you all the success with it. That Skyview is a pretty nice looking kit. Nice to see it sitting up in your instrument panel. And pretty useful too I would think.
Sorry I couldn’t be more help but am a bit out of touch now.
RS232 signalling and TTL signalling should not be confused. RS232 uses a -ve signal as a mark (1 bit) or idle and +ve signal as a space (0 bit). TTL uses +ve as a mark (1) or idle and 0 as a space (0). So a USB to TTL will not work with any RS232 input regardless of voltage levels. An inverter is required.
Most RS232 ports will accept 0V as a mark but IIRC the specification says this is a ‘device not connected’ condition so some ports may need a -ve signal as well as a +ve signal.
That won’t work. The USB device needs to be a host (with the required device driver), so it can talk to the GPS as a slave. Something like this: RS232 to USB Adapter: Connect USB printer to Seria (microcontrollershop.com)
although that is designed specifically for printers and is apparently not bi-directional. If you search on similar products you might might find one that is able to handle generic bi-directional serial communication.
A different solution is an Arduino UNO or Nano with a USB host shield, or the equivalent in another MCU. The available libraries should support GPS communication. You can set it up to initialize the GPS as required, and to match your default RS232 settings. The connection will still be as you have drawn it, with the 5v power from the display driving both the MCU and the USB. However the data connection to the Dynon will still require voltage level control, although the MCU code will do the protocol conversion.
A GPS receiver that supports RS232 is going to be a simpler solution.