MK-312BT BOM Error


I believe I found an error in the BOM for the MK-312BT V1.2 as seen here and the BOM list on the mouser website, here On all pages of the spreadsheet, U10 and U4 are described as LM358N ICs with matching part numbers of “512-LM358N” or “926-LM358N/NOPB”. Yet when searched for in the mouser BOM neither of those part numbers is found and the closest matching result is a “863-LM358NG”, a device from the same series and probably one that functions correctly for the 312 design but either the spreadsheet or mouser part list should be amended. The “863-LM358NG” is also listed as EOL aka “End of Life: Scheduled for obsolescence and will be discontinued by the manufacturer.” so a functional substitute should be found and replaced on the sheet/mouser. The interesting thing is that searching mouser I did find the exact part 512-LM358N for sale. Maybe this is a recent listing that wasn’t available when the spreadsheet/mouser project was made? Little curious if this is an intentional substitution for the 512-LM358N as the other parts were determined to be better. If anybody knows if the correct part to by is the “512-LM358N”/“926-LM358N/NOPB” like the spreadsheet says, or if the correct one is the “863-LM358NG” like the mouser project has listed please let me know. Also who ever has control of the github repos should be made aware of this, if they’re not already reading this.


Finished with checking the BOM on mouser against the MK-312BT V1.2 spreadsheet. Found one other error. The spreadsheet calls for 2 white button covers and 2 gray button covers, both of similar part number “611-BTND600F” and “611-BTND610F” respectively. The mouser project BOM instead lists 4 white and 0 gray. To have your build look like the pictures included in the mk312-bt github repo and all the files I’ve been talking about, you need to remove 2 of the white button covers and add 2 gray ones “611-BTND610F”. Other than that all the parts correlate. One suggestion would be to but the lead acid battery on digikey instead of mouser as its $10 less on digi ($20) and if you include it in the order of the LTC 1661 DAC and ribbon cable from digi it shouldn’t cost you any more in shipping compared to if you just got the DAC and cable.


Thanks, I’ll let the engineers who maintain the BOM know.


Does anyone have a link to the BOM for 1.3r boards? I’ve started making mine up and have hit a few differently valued resistors and one that just doesn’t exist on the 1.2 list. Before I start ordering the ones I’m missing I want to go through and double check the nothing significant has been altered. A few resistors changing value I can deal with.

(Edited to change 1.3 to 1.3r for clarity)


Today, a 1.3 version of China came from China. I also ordered components according to the BOM for version 1.2 + the changes listed below in the documentation. Within a few days I build the board and I will know which parts do not match the list.


Let me know how you get on. I am making up a similar list of differences. Interestingly the BOM seems to have been updated to include the some of the changed resistors in terms of number in the order, but not in the description.


Ok, finished the resistors
Differences on 1.3r board
R7 & R8 - 2.2k on board, 4.7k on 1.2 BOM
R62 - 1k on board, doesn’t exist on 1.2 BOM (add 1 to quantity with R14, 15 & 19)

Capacitors I’m still working on. The ceramics all seem to be correct.
If the electrolytic capacitor values are minimum values then the BOM is ok, but C8 is 6.3V 10uF on the board. The BOM doesn’t specify a voltage, but 50V is sent by Mouser with the BOM’s manufacturer number. Also links to a 50V component with same number through RS Online… I’m not sure if this is an issue but it struck me as quite a bit over.

(Edited to change 1.3 to 1.3r for clarity)


Me again :slight_smile:

More differences on 1.3r from BOM on Mouser:

D4 D1N4004 not on BOM - order extra 1 as for D1
U14 has been replaced with U5 - Still LM2941 but is T and not CT - not a big deal if you are confident bending the legs.

And that’s it. Once the bits I am missing arrive I should be done with the soldering part and will be moving on to software. Irritatingly Q7 and Q8 are back-ordered and were due delivered 5 days ago.

(Edited to change 1.3 to 1.3r for clarity)


Wait, do we talk about the same board? I made the entire V1.3 ( and no differences compared to the parts list I ordered, I did not notice.
There is no D4 diode or resistor R62 in my board. I’m confused.

But I have another problem, I have compiled the whole board of the firmware and the board is reporting error 20. In the official manual ErosTek writes: “20 Calibration Error - Allow ET312 to reach room temperature before powering ON.”
I do not know how to understand.
I have tried the firmware from these two sources and everywhere the startup ends the same way.


I will add my information: programmable fuses have been set according to the manual. LOW FUSE: 0xFF HIGH FUSE: 0xDC
I checked it a few times.


I’ve got 1.3r boards from May 2018. I didn’t get them made up so can’t link to the source files. Evidently there have been some revisions.

There’s another thread about Error Messages 20 and 21 - Differences between the original 312 power supply chain and the MK312BT



I got my v1.3r boards some day ago from a user here.
I checked the board and the BOM which is available in github. Here is the summary of all found differences. (Some are mentioned above, but just to summarize)

ID * in BOM 1.2 * on board 1.3r * comment

R61 * — * 100k RES * new?
R62 * — * 1k RES * new?
R7,R8 * 4,7k RES * 2,2k RES * correct changed?
R13 * 47k RES * 4.7k RES * like R9
U14 * LM2941 * — * where has it gone?
U5 * — * ??? * which component?
U8A * optional * optional * needed?
JP3,JP4 * — * 2x1 SIP Header 0.1" * +12V/+5V what for?
JP2 * — * 4x1 SIP Header 0.1" * how to use and connect?
D4 * — * DIODE 1N4004 * new?

Thats a list of questions and differences I found when comparing BOM 1.2 and board 1.3r. Can anyone give me details and answers to all the differences? How to change the BOM to order all correct parts?

Thanks in advance.


Hi there. Yes, the BOM is not accurate for the 1.3r board. Follow what is printed on the board and it will all work :slight_smile: At least it did for me…

R61 and 62 are new.
R7 &R8 are changed to 2.2k. Go with it.
R13 now 4.7k
U14 is now U5 - upper right corner
U8A is not needed
JP3 and JP4 - wasn’t quite sure of that one myself. Didn’t use them and it didn’t make a difference. Possibly power supply to flash the chip on board?
JP2 - seems to be an option way to wire up an audio input. I didn’t use it.
D4 is new

Just add the parts you queried to your order. I ended up short in 1uF and 0.1uF capacitors but I am not ruling out that I dropped a few or the cat snuck off with them.


I guess I’m blind but now I’ve noticed it. Where can I get the documentation for the 1.3r board? Only the documentation for version 1.3B can be found on the official sites I know (


I got my boards from @voncosel and have not seen the 1.3r Gerbers etc.


I’ll see what I can do about getting the repo updated. I’m so busy on Buttplug that I’m not exactly sure what state everything for mk-312 work is in. :expressionless:


LTC1661 has appeared on Mouser as a PDIP8 package.

At present the 42TL004-RC transformer is on backorder at Mouser. :angry: Does anyone have a couple of spares to sell me?


I’m waiting on transformers from Mouser with an EDD of Dec 1st. The last ones I ordered actually showed up several weeks earlier than the estimate. From ordering all my parts to completing it took 5 weeks.