Bill Of Materials

Details on parts to build your own. Under construction

As long as the ESP32-S3 CPU module of choice has enough output pins, either natively or through an i2c extender module, and it has at least one USB port that supports OTG, it should be usable.

I plan to produce a PCB and have settled on a set of hardware to fit inside a 2.5" x 4" x 1" enclosure. I decided to use 8 LEDs for status rather than the OLED display but one can be added later using the ic2 bus.

Below is the link to specs that match the clone ESP32-S3-DevKitC-1 N16R8 board I got online, 3 for $18. Not using the PSRAM so can use a lesser version. The N8 version with no PSRAM should work as well. The current image size is only 354Kbytes. The 32K version (N32R8) is a bit different but might also work.

https://mischianti.org/vcc-gnd-studio-yd-esp32-s3-devkitc-1-clone-high-resolution-pinout-and-specs

The 8MB SPI PSRAM is not enabled by default. If it was, it would use pins 35, 36, 37. 2 of those I am using for LEDs due to the physical location of the pin vs LED mounting point. The LEDs would have to move to alternate available pins if PSRAM was enabled and we only have a pin or 2 left over. The RGB is powered off 5V not 3.3V as the original board does.

Displays: You can have no display, or with some relatively simple code added, an SSD1306 OLED, or the color LCD in the M5AtomS3 (though code is needed to support i2c expansion IO). You can add in your own display code if you want something different. At startup I poll the radio for frequency, mode, extended mode, time, location, UTC offset, and then calculate the current grid square to 8 digits. It is shown in the debug. Adding a display would make that available on the unit.

IO pins: There is no reason you can't change the total number of IO pins as long as your hardware has free pins available. Adding 2 more pins to each group (Band Select and PTT groups) is the easiest to do since the patterns are represented in 1 bytes values. Adding another group of 8 would be the next step. I have other Band decoder projects that already support more pins, on several IO devices, but this project is a more targeted and simplified project starting out with 6 pins per group to match the IC-905's 6 bands. It also needs to be set to something well defined to work on a PCB.

As the PCB is designed a schematic and PCB layout will be published along with the full list of parts needed for the PCB version.

For now here is a simple list

1x  ESP32-S3-DevKitC-1 - Clone used here, was easy to add the 5V USB host power with a resistor.
2x  2.1mm x 5.5mm power coaxial jacks
1x  LM78L05 5V regulator
1x  1N4000 diode for power to 5V regulator
1x  0.15A resettable fuse on input to 5V
7x  0.01 caps for the regulator(2), PTT input, DC power jacks(2), CPU module 5V, ADC brightness pot input
1x  10uf 6V electrolytic cap for the brightness pot.
1x  22uF or greater 16V electrolytic cap for the regulator output
1x  1K 0805 size SMD resistor, soldered across the DevKitC-1 5v and USB Host Vbus isolation diodes to supply 5V to the USB host cable
1x  Right angle Phono jack for PTT
1x  green LED
1x  red LED
6x  blue LEDs
1x  10K vertical PCB mount pot
2x  ULN2803A octal drivers
1x  PCB
1x  1A resettable fuse for 12V to the relays
1x  Optional 28V DC-DC converter to power a few 28V relays
1x  right angle PCB mount HD 15-pin female D-Sub connector (aka VGA connector)
1x  Plastic or aluminum case, drilled for the LEDs and end panel connectors

Assuming the decoder is to be mounted on the top or back of the 905 controller.  Otherwise adjust the length of the cables
1x  Mounting bracket of some sort
1x  6" DC power cord with 2.1x5.5 coaxial power plugs to connect radio to box
1x  6" PTT cable, 1/8" stereo plug on one end, phone plug on the other, tip and ground. ring not used. 
1x  6" USB Type C to Type C cable.  Suggest one or more snap-on ferrites be snapped on.
1x  HD 15-pin male D-Sub connector.  I like to use the breakout version which offer 16 green micro terminal strips inside the cover, no soldering required