Low cost DIY Frsky 8ch receiver

I've recently been making the switch to running all my planes on the Frsky protocol since buying a Taranis QX7. To date, I've been flying cheaper DSMX receivers in my foam planes with a module on my radio. A friend of mine gave me some low cost receivers that he purchased from Banggood.com to try out. One was a 4ch which I have been running in my Goblin with great success. That said, I prefer at least 6ch radios so I have a few spare channels to add lights, separate channels for ailerons and most importantly, a lost model beeper (I fly over a corn field at my club). In comes the other receiver he gave me. Its an 8ch receiver that is just the board, no pins. I think a lot of people use them for quads as it has sbus and PPM outputs. That said, it also has a string of 8 PWM outputs on one side. I decided to make a break out board that used the standard servo header pins as well as some smaller header pins to solder the receiver boards to. Below is the info needed to build one of these receivers. 

Items needed

receiver board purchased from banggood: https://www.banggood.com/2_4G-8CH-D8-Mini-FrSky-Compatibel-Receiver-With-PWM-PPM-SBUS-Output-p-1140478.html?rmmds=myorder

PCB breakout board: https://oshpark.com/shared_projects/Q3kRt6W7

right angle header for servo leads: https://www.ebay.com/itm/1pc-90-Degree-2-54mm-3x40P-Male-Pins-Three-Row-Right-Angle-Pin-Header-Connector/252492439694?epid=597449186&hash=item3ac9b8e08e:g:Y3gAAOSw-itXqDbW

2mm header pins: https://www.ebay.com/itm/10pcs-1-x-40pin-2mm-Single-Row-Breakaway-Male-Pin-header-for-Arduino-DIY-New/223028045295?hash=item33ed81e5ef:g:8-8AAOSwrzxbLNpS

Soldering iron and solder

*a note here. I linked the two headers needed from ebay. They are both coming from china so it could take a while but the receivers are coming from china as well. The thought was since you have to wait for the receivers, might as well wait for the headers and save a few dollars as well. That said, both headers can easily be sourced from the US and could be delivered in a few days if you are ok paying a little more. 

Assembly

This is pretty straight forward. Lots of soldering but its not overly complicated. A few notes though. First thing, take a close look at the break out board and make sure the VCC and GND on the receiver board match up properly. The receiver board can be mounted with either side up but just make sure that the VCC on the receiver board is attached to the center pins of the servo header and the GND on the receiver board is attached to the front row of pins on the break out board. If you look at the board under a light, you can see the traces clearly. It is also marked on the PCB. 

Both headers will have to be cut to length as they come in long pieces. two 3 position lengths and one 8 position length is needed for the 2mm header and an 8 position length is needed for the servo header. I soldered the 2mm headers in place first and then the servo headers and finally soldered the receiver to the board. There is a lot of tedious soldering on this board. There are over 50 solder joints so take your time. 

One final note on the soldering. The header spacing on the RC board does exactly line up with the header spacing on the break out board. I used 2mm headers on the break out board. the RX board uses some strange header spacing. Something like 1.8 or 1.9 and finding headers in those sizes are very difficult. That said, the 2mm is close enough that I didn't have an issue making the connections. I've made of a few of these now and some seem to fit better than others but I was able to make them all work.

Binding

For my QX7 binding was pretty simple. Turn on the transmitter and in the model setup screen, choose D8 mode. Next power on the receiver while holding down the bind button. The light will go solid. Now select "BIND" on the transmitter and once the receiver is bound, it will shut off. power down the receiver and take the transmitter out of bind. Now power the receiver back and it should be working. Check all the channels with a servo. Thats it! 

Final Thoughts

The break out boards need to be ordered in sets of 3 and the headers should leave you with enough parts to build 3 receivers for under $30. I know there are Frsky brand receivers that are 6-7 channel for around $20 so its not a CRAZY cost save. That said, I like to tinker and DIY. If I can save a few bucks in this hobby, I will. Another note, these are cheap receiver boards so I wouldn't recommend putting it in anything other than a cheap foam plane until you are certain its operating properly.