IN-8-2 Modular Rev 3 build - feedback and questions

Happy New Year everybody!


Thanks to Ian's perfect kit, I successfully finished the Modular Rev 3 kit a few days ago. The tubes are IN-8-2s and I chose the ESP-01 as a time provider. Additionally I've attached an RCWL-0516 for presence sensing. I'd like to provide feedback on a few things and also have some questions for the professionals here:
1. The NeoPixels (NP) have to be mounted on the bottom of the tube holder PCBs (at least for my IN-8-2 holders, see images), which is not really described anywhere. The NP have to be inserted in a cut-out of the PCB. However, the cut-outs were to small and had required a lot of force to insert (at least for my taste), so I chose to use sand-paper and widended the cut-outs a bit. Altogether that worked without problems.





2. I didn't like the lit decimal point of the 10s tube, which indicates display switched on again after motion was detected. I commented out the respective line in the code and updated the microcontroller using an Arduino UNO board. That worked without any problems. Maybe that could become the new standard preset in future code revisions?
3. Using a 9V 1A power supply, the HV calibration did not successfully finish (only counted up and never down). After changing to a 12V 1A supply, HV calibration worked.
4. With the standard 180V target voltage, some IN-8-2 showed flickering (not fast) of the filament areas on top and bottom of the actual number (the part between the disks which separate the numbers). When decreasing the HV, this dissappeard. Currently the clock runs at 165 V. All voltages were confirmed by measuring the HV at the respective test points.
5. When the tubes are lit at the lowest intensity (low/no light on LDR) after being blanked for a longer time, some tubes flicker on a off. The flickering vanishes after a minute run time at lowest intensity or immediately when increasing light level on the LDR. I guess the flickering could be diminuished by changing the low-light PWM settings of the clock? (I think the effect was also there at 180V)
6. I'd like to connect a few things to the 5V Vcc of the clock. Altogether that would result into an additional 500 mA peak power drawn from the respective pins. I understand that this might be to much, although the LM2596T is specified for up to 3A total. In a first test, I could successfully power the additional load without any obvious side effects, of course the LM2596T became hotter than normal, so I attached a heat sink. Any late term side-effects that I should think of? In this context: Is there a drop-in replacement for the LM2596T, which is more effective and thus runs cooler?
7. I generally feel a bit uncomfortable when putting everything in a wood enclosure, since I expect the heat dissipation of all the chips to potentionally become problematic. In order to reduce this, I'd like to invest a few € into an IRF840 replacement with lower Rds(on). For example, I could get an TK31E60W , which has a max. Rds(on) of 88 mOhms. However, I am unsure about secondary parameters (e.g. avalanche enery, input capacitance, switching time), could anybody give me some hints if these things are critical in our case?

OK, that was a long first post. Thank you for reading it and I'd appreciate your feedback/comments.

Thank you very much Ty and Ian,

1) It was not really a problem, however it left my confused for some minutes. I don't know if it's feasible to update the manual in this regard?!

3) I'd get another 9V power supply anyways and will test with that again. I remember reading about this point here in the forum (was it Ty?!) and luckily had a 12V supply at hand.

4 & 5) I'll most likely change the firmware on my clock, since I am lazy and don't want to adjust this through the menus.

6) OK, thank you, I'll stick with the LM2596 and supply proper cooling.

7) The 2SK2841 was also in my group of potential IRF840 replacements, unfortunately I don't get it from my preferred supplier. Would be intersted to know why the IRF840 was in there originally? Ian, thank you for the heads up to the IRF640, although reading specs on many MOSFETs I didn't see that one. Too many choices out there. Since I could get that from my supplier comparably cheap, I'll give it a try. One question, just to be sure: Is the max. Vds of 200 V of the IRF640 not a bit thight for the HV circuit?

8) I'd like to add some further digital outputs to the clock for switching the loads mentioned under 6) in my original post. From reading the MEGA328 documentation and looking at the clock's schematic, I couldn't find any free IO ports. I guess they are all used already. However, since we have I2C, I thought about adding an MCP23017 IO expander, but with 16 IOs that might me overkill, although the chip is inexpensive. I'd only need one or two additional digital outputs. Has anybody experience with the MCP23017 or an alternative to realize this?

Thank you!
-Phil