Different animal, but I use an external power supply for the Arduino and associated circuitry for my modified GS/3.

The Gicar board in the GS/3 is difficult to troubleshoot/repair and costs $600 to replace. My philosophy was to not risk shorting any circuits on the Gicar board. An external 24VDC 100W power supply was necessary to drive the gear pump anyway, so I added 5VDC, 9VDC and 12VDC 1A voltage regulators to step it down for various circuits. They're located in a little hub box where everything connect together. The regulators run the Arduino, the manual profiling circuit (touch-sensitive knob, LEDs, etc.), as well as the interface circuits inside the GS/3 brain box where the Gicar board is located. The interface to the Gicar uses AC and DC 5VDC optoisolators to monitor various circuits on the Gicar, and has two 5VDC relays for triggering the brew cycle and a future needle valve bypass solenoid.

The idea was to completely isolate the GS/3 and Arduino circuitry. Besides, it's not clear how much extra power the low voltage circuits on the Gicar board can spare, and I didn't want to find out the hard way. That said, I do tap a 12VDC source on the board to trigger a relay that switches AC to turn on my solenoid steam valve and light an LED ring around the front-panel push button for same (yet another mod.)

Maybe it's cheating, but this looks like an easy solution to add a shot timer:

https://prima-coffee.com/equipment/lumi ... gKHd_D_BwE

Yes, it is a voltage regulator (78M05).

Tapping the 5V pins on the LM will not provide enough current anyway so I will leave them alone. Also as Peppersass mentioned it's probably safer that way anyway.
I'll keep using my external 12VDC power supply for the moment but the AC to DC converter is definitely something I'm going to explore later on. Those are relatively small and some are waterproof with high enough heat resistance so they would fit really well on top of the SSR.

Yes, I saw that little shot timer. Looks quite nice actually.

To be honest the shot timer is more a fun addition to the rest than anything else. I'm still using my lunar scale for that. It might become more useful with the flow profiling mod to see pre-brew and full flow time.
The flow profiling mod can work 100% without the arduino by tapping the 3-way valve for power (new solenoid and microswitch can both handle that easily). The addition of the arduino circuit was primarily to test the autobackflushing idea. And since that works great I decided to power the new microswitch, the solenoid and the arduino with a unique 12V DC supply so I won't have to deal with 110VAC.

One more fitting and I should finally be able to connect the last mod:



I tested it with the microswitch connected to the arduino board and everything seems to work as designed.

Nice! Are the tubing fittings flare, compression or nipple? Can you provide model #s and source for the solenoid valve and needle valve? Is the solenoid NO or NC?

https://www.espressoparts.com/ace-shure ... -timer-kit

Have you seen this yet?? Seems very similar to what you are trying to achieve, biggest difference is you're using flow profiling and they are using pressure profiling.

The creator is very active on instagram and might be willing to offer some advice to you. Love what you are doing here! Just wanted to point out a possible source of knowledge with this kind of "mod"

The solenoid valve is a 3way universal from Granzow (ODE distributor in the US):

http://www.granzow.com/valves/solenoid/A1D40-3UV-A/

The flow factor is a bit on the low side but should still be enough.

The metering valve is from Swagelok:

https://www.swagelok.com/en/catalog/Pro ... =SS-4MG-MH

All the fittings except one are Swagelok fittings making things easier to connect. The downside is that they require a bit more room.

Yes, I saw the work for AceServices. I know they worked on a full mod for the LMLM (not just the Linea). I believe they do flow profiling as well.
I was considering waiting for their mod but it might take forever, the backflush is not available (I'm sure they could do it though) and it is a more "definitive" mod.

The one I'm doing is 100% reversible so far. This means that some things are a bit more complex than they should be. For example I connected the main microswitch (which is now the second one) to the arduino to avoid rewiring it. There is a nut on the NC cable and I did not want to remove it.
If it is long term then there is some things than could be simplified in the design for sure.

I received an improved version of the microswitch 3d printed fitting:



It is not yet perfect but that one definitely works very well.

I also received the last fitting for the needle and solenoid valves:



As shown in the picture there are two small leaks that I need to address before using it.
This was actually the second iteration as the first time the solenoid was plugged in the wrong order and there was no water flowing through. The pump quickly turned off.

This is potentially a less safe way to connect the solenoid+needle valve as it relies entirely on the rotary pump to make sure the pressure does not exceed 12bar. The other location, at the brew group, would have the expansion valve as an extra protection. I might move it there once I receive two extra fittings but there are some downside as well.