Post By Lyrebird
Post By Lyrebird
DIY autofill controller.
I decided to make my own autofill controller rather than replace the blown up Gicar unit in my VBM Junior.
I wanted this to be more reliable than the original, that means no microcontroller, shifting the relays off board so they can be replaced cheaply and keeping mains voltage off the board (an external DC power supply is needed). A second reason is that it is far cheaper to source a switchmode DC supply than it is to include the supply on board*. The 12V supply is at the top of the board, the extra connectors route this via the tank water detector so the circuit only goes live when there is water in the tank. I've also assumed that element control is via an SSR.
With no microcontroller, the autofill circuit is based on a simple comparator using a LM358 dual op amp, the trigger voltage is tunable via the trimpot (I'm on rainwater at the winery so I want it to be adaptable). The second half of the op amp acts as a single sided RC time delay so the water keeps filling for about 2 seconds after reaching the probe, preventing nuisance switching.
The comparator output is fed via some basic diode logic to a couple of small mosfet transistors which drive the solenoid and pump relays, the diodes prevent the solenoid operating when the brew switch is activated and prevent the element from running until the water level is reached. I stuffed up drafting the relay drivers so they are temporarily on veroboard.
The element output is designed to be fed through a temperature controller to the SSR but the existing pressurestat is in the supply side circuit: if no temperature controller is used the pressurestat will act as normal, if a controller is used you simply turn the pstat up so it acts as a second safety (this supply is also routed via the existing temperature cutout).
Lastly there are three LEDS, one green for on, one yellow for empty water tank and one red for the element.
All seems to work on the test bench, now to see whether the machine agrees.
I made a couple of mistakes drafting the board, partially because I got a bit ambitious and tried to cram two controllers on one circuit**. I've redrafted with only one circuit, I'll send the new design out for fab and build one up. The fab house I am using runs an open source board program, once it is working I will add it to their list and post the link here so anyone can get them made. Cost is about $10 a board (but they won't do a batch less than 5). Using the external relays and SSR as shown, it costs about $60 to populate the circuit.
* A third reason is that I am thinking of putting a rotary pump with a 24VDC motor into the machine so it will have a DC supply anyway, a 12V reg is $4.
** I wanted to make it universal but I'm no longer sure that's a good idea. The empty space at the bottom of the board was for the second autofill but doofus here didn't include enough connections. Drafting up a board with enough connections for dual boiler duty I ended up with a board that was more connectors than anything else.
Last edited by Lyrebird; 10th August 2018 at 08:44 AM.
The PCB mob I have been using (Allpcb) have been running a free DHL delivery offer all year so far so boards arrive pretty quick and much cheaper than $10 a piece. My last order went in at 10PM on a Monday and I had the boards by lunchtime the following Monday.
What size is the board ??
Thanks for that, I haven't used AllPCB due to their location: I've had bad experiences with the cheapest option manufacturers before.
The board is 60mm x 75mm (2 1/2" x 3").
Bloody hell ....Is that where He got to!
Originally Posted by Lyrebird
Say Gday to him for Me.!
Its been ages since we last saw each other.
Well 'll be!
Well it looks like the machine does agree.
SSR, relays and new board mounted on a aluminium bracket where the old Gicar unit attached. Everything seems to be functioning as it should.
BTW I took the opportunity to fix some of the dumber bits of VBM's wiring like using a PVC insulated wire on top of the boiler with no standoff (the level sense earth return). The replacement wire is ETFE insulated high temperature wire, mounted on a 10mm standoff.
I also completely stripped and cleaned the boiler and all fittings and made a little insulating jacket from silicone foam with a neoprene outer.
I'll send the revised boards out for fab, make one up and test it out then I'll post up the design on the sharing page.
A couple of things will change: I'll make the level probe wires pluggable to ease fitting the board and I'll increase the value of the current set resistor for the "On" LED. Damn that thing is bright.
Last edited by Lyrebird; 13th August 2018 at 03:51 PM.