Eggfinder Bluetooth- 2022

Aug 19, 2012
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Hi all,
Just a quick thread describing my initial experiences with the Eggfinder Mini trasmitter with Bluetooth kit. More than anything, I'm writing this to document what software works in 2022.

I'm a longtime user of Telemetrum, but the board was too big for my 24mm min diameter rocket. Having previously built the Quark and WiFi switch from Eggtimer I was fairly well prepared for building this kit. I use a 4X magnifying visor, a 1/64" solder tip on my Weller soldering station.

I bought the following Eggfinder kits:
Basic Bluetooth Package for use with your Android Device ($103 with Mini transmitter):
and added the data cable for transmitter debug:
Data Cable (for flash-updating Eggfinder LCD): $5
I forgot to buy this the first time around, and would recommend it:
Antenna Combo: RP-SMA + 3 dB external antenna: $12

The mini transmitter went together nicely, and not wanting to bridge the two switch terminals permanently, I soldered in a little wire to bridge the two "RUN" pads, which I would regret later when debugging the Receiver- it worked for the first day, but detached later in the Receiver debug. I installed VisualGPSView, connected the data cable, and started watching the stream of GPS data coming off of the chip's serial output. I have to say this was cool to see, and to see how much processing the GPS module was doing. I didn't have a 2S Lithium Ion battery laying around, so I soldered in connectors for two 1S cells in series:

The Receiver went together fine as well, though the BT portion of the instructions have a photo missing. The BT module plugs in using the supplied 4 wire cable into the 4 pin header, to save space I bent the 4-pin header as shown here:

I don't like how large the antenna is, relative to the stubby that comes with the transmitter, and need to send Cris a note about what he thinks about a stubby antenna for the receiver side. My intent is to model up a small case in Fusion 360 and 3D print it for direct attachment to my phone. Pairing the BT was easy, and the instructions give the BT-04 name, and passcode of 1234. Do follow the instructions to confirm that you get the appropriate lights blinking on the transmitter and receiver- this is how I found my bridge wire had become dettached.

From the cellphone software side, RocketLocator is a no-brainer (also see their website,, and works well on my Samsung Galaxy S9. The app is really nice, and you don't have to enable the mock location app in the Developer Options on your phone, though this worked without issue before I found RocketLocator. The app automatically downloads the satellite photos, though their FAQ advises to zoom in on your launch field if you don't get an internet signal out there, so that those images are cached. The screen shot below shows my house, with my cellphone as the blue dot, and the transmitter as the red dot. The faint blue track shows me walking the transmitter out to the back fence and back. Pretty sweet!


I haven't flown the unit yet, but will do so in the next 1-2 months for an attempt on the club's D & E altitude motor records.

All and all, outside of a bit of stress of finding what software would work on my cellphone, the assembly process was fairly easy, and I learned a thing or two along the way.