Arduino based SDR milestone
Mike Lewis
I am headed north in a couple days and that brings my rapid development cycle on my version of a Teensy 4.1 based SDR to a close. I hope to continue working on it after I return to Camano but I may be working some longer hours for a few months at my part time job.
It uses a Teensy4.1, the audio card a Si5351, and optionally a RS232 TTL converter for CAT operation in pan-adapter mode. The display is either a 4.3” or 7” capacitive touchscreen using the RA8875 or RA8876 display controllers. I have implemented my own touch gesture engine and have a smooth working touch, press, drag and swipe experience. With the 7” display, I am not using any knobs and have not been missing them. On the smaller size I am using I2C bus connected encoders with RGB LED inside them to light up they knobs for more feedback and cool factor. It is very easy to build and wiring is minimal if you stack the boards.
I do not have Transmit hardware I yet though the UI and underlying table driven structure has support for that when it arrives later. All UO elements are table driven meaning they can be resized and moved about without recoding. There might be some font changes required here and there. The same code for the most part runs on both the 4.3 and 7” with very few configuration (table value) changes due to the 1024x600 layout vs the 800-x480, as you get more space.
It is also a very functional pan-adapter for a K3 with a serial CAT connection which tracks the VFOA and B, center frequency shifts, and major indicators like filter, AGC, Mode, Antenna selection, and TX status. It normally listens to status messages sent out by the K3 set to auto-info=1, but if it sees a new frequency, it then polls for an immediate update in case the VFO is moving still to better track a spinning VFO without constant polling when it is idle. My goal is to remote control and be a pan-adapter for a FT-817 but that requires a RX capable of 63Mhz which I do not have yet. I do have a iFaceV2 IF buffer board arriving soon to tap into various radio’s IF more easily.
I have a Hermes Lite V2 on the way which is headless with ethernet connection. I plan to implement the ethernet openHPSDR protocol to use my SDR as a control head for it, no PC required. There is a Pi version out there, PiHDSDR.
Lots more planned, like transverter support, but it is quite usable as it stands today if you are looking for something different.
My project GitHub site is at K7MDL2/KEITHSDR: Teensy4.X with PJRC audio card Arduino based SDR Radio project. (github.com)
Lot of info on this version build Changes on GitHub SDR-RA8875 (groups.io). Also check the forum Wiki pages and also my GitHub Wiki pages for info on libraries and construction notes. At least 2 efforts are underway to design a PCB that mounts to the back of the display.
There is also a simple “backpack” version with smaller display and interface. My version went the deluxe model approach 😊. I am taking advantage of the RA887x display controller graphics features for screen scrolling to draw the waterfall and spectrum.
I would like to point out the great work by Bob, W7PUA on helping us be able to run the audio library in full 32 bit floating point mode. Previous versions were 16 bit integer and he has been converting the library as we go. We are now running with a 4096 point FFT with I and Q. My 1024 pixel 7” display only shows ¼ of the data available and that is about 25Khz at 104K sample rate. We can go higher if needed and eventually will have pan and zoom features.
I have 2 of these built, a 7” with QRP-Labs Rx board, a SV1AFN 10 band preselector, switched Preamp and digital step attenuator. It is packaged into a sloped front box and awaiting an aluminum front panel from FrontpanelExpress.com in Kent, WA. The 4.3” is packaged in a smaller case and is targeted at pan-adapter and/or control head duty for a FT817, K3, or the HL2 SDR. it does not yet have an Rx hardware. It has 2 RGB I2C encoders. For radio mode it supports high resolution encoders for the VFO.
Part of this build has been spent on trying to use an 10Mhzx OCXO or TXCO with the Si5351A version and a C version board, and testing different libraries. Mixed results so far regarding drive levels and output noise at certain frequencies. Ray W7GLF has begun looking at a new C version boards with some nice enhancements. I have 1 C version here that is working.
Some teaser shots attached with captions. One form Feb is the starting point. Just a few changes made since 😊.
73,
Mike
K7MDL EL87sm & CN88sf
Loren Moline WA7SKT
Sent: Saturday, April 24, 2021 6:43:50 PM
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Subject: [PNWVHFS] Arduino based SDR milestone
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