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MK-312BT V1.3

Documentation at :

Forum (for questions/discussion): (Estim Specific Category Here, but may not include all estim messages)

Board ordering instructions

Preferred board house is

You'll need 2 gerber zip files from the gerbers directory (click links below to download):

NOTE: Order Front Panel and Main Board as seperate items (but they can be in the same cart), due to difference in "Different Design" setting. See below.

  • 2 Layer PCB and Dimensions should be detected when you upload the zip with the gerbers
  • Quantity: No requirement, choose whatever you like
  • Thickness: 1.6
  • PCB Color:
    • Main Boards: No requirement, choose whatever you like
    • Front Panel: Black is recommended, but not required. Choose whatever you like otherwise.
  • Surface finish: HASL
  • Copper weight: 1oz
  • Gold fingers: No
  • Material: Standard FR4
  • Panel by jlcpcb: No
  • Different Design
    • Main Boards: 2
    • Front Panel: 1
  • Remarks:
    • Main Boards: V Score the Main Boards panel as indicated.
    • Front Panel: Place all Fab Markings (Serial Numbers/Date Codes) on the BOTTOM side of the front panel board.

Board Assembly Instructions - IMPORTANT

  1. Trim Potentiometer knobs to correct length if desired
  2. Use black permanent marker to black out front panel hole walls if desired
  3. Cut the tabs off of the base of the pots so the board sits flush with the display facade if desired
  4. To correctly fit LCD - solder header to LCD board first. Next insert LCD panel into front panel daughter board. Then put screws on front panel facade and finger tighten M2.5 screws first. Adjust positions as needed so everything lines up and sits well. Finally solder LCD header to front panel daughter board.
  5. Make sure Pin 32 (LED2) on the HC-05 module is actually soldered and making connection to the ZS-040 break out board or "Radio" LED may not function on the front panel
  6. Be very careful not to bridge pins when soldering the LM 2941 (U14). Apply heat to 1 pad only and carefully apply solder. If a bridge occurs - remove the IC, clean the pads throughly with flux and solder wick and then retry. Pins 2 and 3 can be bridged because they are both ground. Ensure that no other pins are bridged. Check with multimeter continuity tester for bridges before power on!
  7. Make sure to check the orientation of all electrolytic caps. (+) indicates the positive and a solid white "|" indicates the negative.
  8. MAKE SURE YOUR POWER PLUG IS CENTER POSITIVE OR THINGS WILL GO BADLY. If you fuck up and plug in a reversed polarity supply - replace electrolytic caps C1 and C4.
  9. Please remember to adjust the LCD contrast potentiometer - if incorrectly set the unit and backlight will power on but the interface will not be displayed.
  10. Place transformers with P facing the output jacks (yes we are using the transformers "backwards" if you follow orientation given in the transformer datasheet )
  11. Trim pins of 4066 IC (U3) Socket on the front panel board flush before soldering so buttons can clear. If the buttons still interfere, carefully disassemble the button and cut off the bit of the plastic housing that interferes with the 4066 IC socket pins.
  12. Using side cutters cut off the screw boss/screw mount on the case that touches/interferes with the ribbon cable socket on the display board.
  13. The LCD display has metal retention tabs that may short the soldered leads of C43. When installing the display board ensure that this does not happen (shorten the capacitor leads and bend the offending metal tab out of the way if necessary
  14. If Error 20 is encountered on first boot:

MK312-BT Firmware

  1. We are using an external 8mhz crystal instead of the internal RC oscillator that the original uses. We need to set the fuses to enable this.
    • LOW FUSE: 0xFF
    • HIGH FUSE: 0xDC
  2. A patched version of buttshock-et312-frankenbutt-f005 is recommended.
  3. The firmware needs to be changed to replace the up/down arrows on the UI with left right arrows (this is because the LCD we use has a different character set)
  4. Obtain or modify a copy of the firmware and flash the result onto the AVR.
  5. If you don't want to use an external crystal - we need to set the calibration byte for the internal oscillator. If programming a blank chip you first need to read the calibration bytes of that part (i.e. using avrdude -t “dump calibration” the fourth byte is the calibration byte for 8MHz or use atmel studio to read the oscillator calibration byte). Then program that byte into 0x3fff in your firmware. These bytes will differ on different chips even from the same batch. The firmware reads that byte to set OSCCAL on startup. If the byte is inaccurate various problems and failures will occur related to timing, interrupts, and serial communication. Just use an external crystal dammit.

MK312-BT Original Fab Notes

(These are the old fab notes from the repo, mostly kept here for history sake. Ordering instructions above cover most of this.)

Main Boards

  1. V Score the Main Boards panel as indicated.
  2. Main Boards has 2 board designs panelized on 1 panel.
  3. Thickness is standard 1.6mm (0.063inches)
  4. Board is 2 layers
  5. HASL Finish - Pb Free Preferred if possible, otherwise Pb HASL is OK
  6. 1oz copper
  7. FR4 material
  8. Main Boards : Green solder mask, White Silkscreen (silkscreen BOTH top and bottom sides)
  9. ITAR : NO
  10. IPC-A-610 - Class2 (If possible - otherwise ignore)
  11. Main Board Dimensions : (193.04mm x 104.14mm) or (7.600 inches x 4.100 inches)

Front Panel Boards

  1. Place all Fab Markings (Serial Numbers/Date Codes) on the BOTTOM side of the front panel board.
  2. Thickness is standard 1.6mm (0.063inches)
  3. Board is 2 layers
  4. HASL Finish - Pb Free Preferred if possible, otherwise Pb HASL is OK
  5. 1oz copper
  6. FR4 material
  7. Front Panel Boards : Black Solder Mask, While Silkscreen
  8. ITAR : NO
  9. IPC-A-610 - Class2 (If possible - otherwise ignore)
  10. Front Panel Board Dimensions : (196.85mm x 58.72mm) or (7.750inches x 2.312inches)

Bluetooth Serial Configuration

Refer to for more information.

// Test command to check if we are communicating (expect to receive OK)

//Name the module

//Set baud rate to be same as the ATMEGA16

//Set the pairing password

//Set the LED Indicator polarity (1 = High Drive 0 = Low Drive)

// Reduce power consumption by increasing the scan interval. Without
// this it consumes ~43mA when not connected and causes the 5v regulator
// to get toasty (but still within operational temp range)

To do this automatically:

  1. Solder Pin32 of the HC05 module (See bluetooth/HC05PINOUT.PNG for reference)
  2. Flash the included bin file onto the ATMEGA16
  3. Plug the HC-05 bluetooth radio into the board (ensure pin 32 is soldered to the carrier board)
  4. Place HC-05 in command mode by holding down the button on the HC-05 module, power up MK-312BT and release button after 2 seconds. LEDs on HC-05 will blink slowly (0.5 Hz) to indicate command mode.
  5. Watch GUI until it says the HC-05 configuration is finished and flash normal firmware back on to the ATMEGA16
  6. If program stops on "Communicating with HC-05" make sure OSCCAL value for 8 MHz R/C position is copied to &H3FFF of bin location or use external 8 MHz crystal with appropriate fuse bits set (FFS use the external crystal)

3D Printable Case

STL files for a 3D printable case for the MK312 are available in the case/ directory. For hardware, this case requires:

  • 4 M2.5x20 screws
  • up to 3 M2.5x5 screws
  • some dampening for the battery (double sided foam tape may work)