Building your own TTL Converter for FRSKY Interfacing

[Rob Thomson]

One of the requirements for getting the FRSKY Mods to work is the use of a TTL Converter.

Fortunately we have plenty of off the shelf options for this; however some people who are so inclined will no doubt want to build their own convertor - from the ground up.

The following circuit shows how to put this system together:

frsky-ttl-interface.png (17.98 KiB) Viewed 6929 times

This circuit can be built quite easily on a small piece of breadboard.

[Flaps 30]

That is the circuit that I am using. I have plenty of PNP and NPN transistors around the place and this circuit really isn't that fussy as to the type numbers, any old transistor should do the job I ended up using BC212 (PNP) and a 2n3904 (NPN). To keep my wiring neat I made space on the stripboard to install a 78L05 voltage regulator feed the circuit. The supply to this came from the + volt pin of the transmit module. Wire used was some old 'rainbow' ribbon cable that I had in the junk box.

[chrispaiva]

I did mine using a MAX232 IC with 5 capacitors of 1uF !

The schematic can be found here
http://sodoityourself.com/max232-serial ... converter/

I drew a little pcb with PAD2PAD Software
http://www.pad2pad.com

Check the results ! It was my first try with pcb and soldering components.

[JEANALTAYR]

hy i did mine with classics and smd spare parts on a veroboard
jmi

[MikeB]

Looks like either an old chip or an old circuit, more recent MAX232 chips work with 0.1uS ceramic caps.

Mike.

[Oshb5ems]

HI
I also used the max232 and 5 caps for a TTL to PC connection but this was for my Astronomy mount So its nice to know it will come in handy for the radio.. If im not mistaken I also used a aurduino bluetooth module so i could get it to work wireless I will have to see if I can get the bluetooth option to work on the radio.. The only thing is my mount provided the voltage to run the BT module so I would need the specs for the radio before trying it. But then again if it runs the max232 with caps it should be ok to run the BT.. I will have a look and get a copy of the circuit diagram and put it up on here to see what you think....

Andy

Andy

[ShowMaster]

I found the max232 SMD boards on ebay and a great post showing how to modify them for er9x. I bought 5 and it was less than $20 to my door. I did build up my own in the past but I can have one of these ready to install in 15 min( removing the db9 takes a few min) and they are so small and work every time. I tried the Frsky modified lite boards and couldn't get them to work and the cost was more to my door and all that waiting time to get them. The ebay boards came in 4-5 days with free shipping.
If interested I'll look up my source and the mod post. Built up is good but this ende up the size of a large stamp.
SM

[Oshb5ems]

When I made my max232 one I originally used wire frame and then encased them in hot glue but the power reg I was using melted the glue so I found a small electronic kit box to put it in one. Mine for the mount I was using worked via a 9pin D from the laptop out to a RJ45 which plugged into the mount in place of its handset. Hence using the Bluetooth Arduidino module enabled me to do away with the 9 pin din and I hard wired it so it fitted inside the mount so the mount look just the same as a normal mount.. (what made it possible was the module was already TTL out which I only found out when trying to just add the module to the front of the max232 circuit. and when t did not work I had to find out why So it was all good in the end.)

Bluetooth Module with TTL out.

BTsmall.jpg (21.06 KiB) Viewed 6702 times

the pins are 5v +Ve, GND, TX TTL and RX TTL

Andy