How To: BrewPi LCD Add-On

bLazem · Jan 25, 2015

doomy86 said:
The backlight controller is just pin 2 from the shift register trough a 220 resistor on the gate, 5v on the collector and the emitter straight to pin 15 of the LCD.

Ah this! Didn't look so well, sorry about that.

Ok so as I said before I'm an electronics beginner and I don't know what this means by the 'gate' and I assume the 'emitter' and 'collector' are terminals on the rotary?

If you could be so kind as to add that to the latest schematic, that would be awesome.

Great thread man thanks for doing all you have done here! This project has taught me a bit about electronics and raised some interest for sure.

doomy86 · Jan 25, 2015

If you look at the datasheet of a 2N3906 PNP transistor, you see 3 connectors:

https://www.fairchildsemi.com/datasheets/2N/2N3906.pdf

Gate -> 220 ohm resistor -> pin 2 of the Shift register
Emitter -> to pin 15 K of the display
Collector -> 5V Power from uno

day_trippr · Jan 25, 2015

bLazem said:
[...]If you could be so kind as to add that to the latest schematic, that would be awesome.[...]

Umm...that wasn't me...

Cheers!

day_trippr · Jan 25, 2015

Here's an updated schematic for my BrewPi shield design including both the original BSS84 P-channel FET for the LCD backlight dimmer feature, along with what I gather doomy86 did using a PNP transistor and 200 ohm resistor to implement a backlight dimmer.

As noted, with either backlight dimmer option present, the LCD will wake up if Uno pin D7 is grounded (usually by the pushbutton on the rotary encoder switch)...

Cheers!

[edit 02/05/2015: corrected P-FET G/S pin swap]

bLazem · Jan 26, 2015

Awesome!!

That's great news. So stoked on this, thanks for the update!

MrSaLTy · Jan 26, 2015

Day_trippr, maybe I missed it somewhere but what is 'SI option' ?

day_trippr · Jan 26, 2015

MrSaLTy said:
Day_trippr, maybe I missed it somewhere but what is 'SI option' ?

Oh - LOL - I had been leaving that out of the posted schematics but this time forgot to remove it.

Back at the beginning when I threw all the parts on a bread board I poked around with a 'scope looking for signal integrity issues that might explain why some folks were seeing character errors on their LCDs.

The HC series dates back to the 80s and was one of the early high performance mixed technology families. To get there they took pretty much all of the damping out of the front end and shifted thresholds lower. The result is the parts definitely do not like negative overshoot on clock signals, as the positive recovery can cause false triggering - while still being well below the minimum specified switching threshold.

And I was seeing a solid 1.2 volt overshoot on the signals from the UNO to the shift register, and a pretty hefty bounce back. While I wasn't seeing character errors on the LCD it looked like that was just a matter of time. By inserting 33 ohm series resistors in those three signals, their edge rates are slowed enough that the overshoot is almost totally removed.

This overshoot isn't present on my shield boards, likely due to the very short wires (in the inch range, vs the 8 inches for the Dupont jumper wires), so I've been leaving those resistors off the boards and the drawing....

Cheers!

MrSaLTy · Jan 26, 2015

Thanks for the answer. Looks like the BSS84 pfet only comes in a SOT23 package. At least thats all i'm finding. Now to figure out how the hell I'm going to use that....

day_trippr · Jan 26, 2015

LOL! Yes, they are tiny little effers. I have to put on my magnifier headset to have a prayer of even finding them.

You could follow doomy86's lead and use a 2n2906. Those can be had in all kinds of through-hole packages...

Cheers!

MrSaLTy · Feb 5, 2015

day_trippr I was looking at your latest schematic and trying to wrap my head around how this works with the PFET in there and I have a question. Since this is a PFET don't we supply V+ to the source and control it from the gate? You have 5v at the gate and pin 2 of the shift register going to the source pin. Is that right or am i thinking about this the wrong way? I'm just trying to understand how this works. Thanks for putting up with me.

day_trippr · Feb 6, 2015

Whoopsie! Drawing error, thanks for spotting it.
I've corrected the drawing...

Cheers!

day_trippr · Feb 11, 2015

So my rotary encoders finally arrived from China having taken four weeks to float here. Ironically there is now a competitive supplier on Amazon Prime - two day delivery. <sigh>

Anyway, wired one of the switches to my debug BrewPi minion in no time and it worked perfectly. Press the button and you can walk through the settings and change them if desired. Could be handy when I'm down in the brewery and want to change something without running back up to my office or using the keezer RPi monitor.

Then it was time to solder in the BSS84. Though the SSD designs I create actually have hundreds of parts that make a BSS84 look huge, it's still hella small when your eyes are 60+ years old

But I got it installed cleanly and now everything works as expected. The LCD backlight shuts off in 10 minutes and will light up when the rotary pushbutton is clicked. Very cool feature that should extend the LCD display lifespan.

When I get a chance I'll see if I can take a macro shot of the BSS84 soldered to the back side of the protoshield. Hopefully it'll be more than just a black speck. I need to buy one of those USB microscopes, I think...

Cheers! :mug:

MrSaLTy · Feb 11, 2015

Hopefully my encoders are on the same boat yours were

Should get my BSS84 pfets tomorrow. I would be interested in where you soldered yours if you do have a chance to get a pic. Thanks again Day_trippr!

day_trippr · Feb 11, 2015

In case I don't get to it quickly (or if the pic turns out crappy), here's what I did:

While my schematic shows the p-fet between the shift register pin 2 and the first diode, it can go anywhere in the series connection from SR to LCD. And the easiest place to stick it was between the diode and resistor as that had a short (.1") wired connection.

So I removed that short wire connection on the back of the protoshield and soldered the p-fet in its place, rotating it around 30° or so to line up the pins. That put the gate pin over its own via which made wiring to the shift register output easier than soldering straight to the tiny p-fet pin.

Piece o' cake

Cheers!

MrSaLTy · Feb 15, 2015

Ok that was a PITA. My close vision is not what it used to be. My soldering Isn't what it used to be either heh. Some sorta big blobs but hey it works. Took your placement advice Day_trippr. Here is a crappy phone pic.

day_trippr · Feb 16, 2015

Perfect - exactly how how I did it, just slightly smaller blobs

Well done! :mug:

andrewmalizia · Feb 16, 2015

day_trippr said:
Perfect - exactly how how I did it, just slightly smaller blobs

Well done!

Awesome stuff. I've been using a simple temp control circuit with the ethernet shield for a while now and logging to Xively. But I'm moving over to brewpi because I have all the stuff sitting around, great post!!

Day_trippr....
Is this the encoder youre using? http://www.amazon.com/dp/B00KHTLWU6/?tag=skimlinks_replacement-20

Have you done much design of PCBs? I'm thinking this would be a pretty simple PCB design since Elco stopped the production. The project could be uploaded to OSHPark and had for about $10/board. I may work up a design if I find some free time.

For the folks that are having a hard time with soldering...
If you are using a radio shack pencil, I HIGHLY suggest you get a soldering station. Places like circuit specialists have analog or digital adjustable stations for $30-50 usually. I cannot stress enough how much this changed my interest in electronics. I was so frustrated before with the radio shack pencils. I went through like 4 of them, a total waste of money. Now, with the station, its a 1 second hold and then apply solder. Beautiful joints, every time.

I also use a hakko brass ball tip cleaner, this is about 100x better than a wet sponge as it does not reduce the temperature of the tip.

I realize I'm telling everyone to spend more money than they probably want to, but if it seems like something you'll stick with, you definitely want to make these changes.

andrewmalizia · Feb 16, 2015

And as a clarification, there is really no point in the pfet if using the rotary encoder right?

MrSaLTy · Feb 16, 2015

andrewmalizia said:
And as a clarification, there is really no point in the pfet if using the rotary encoder right?

Depends... With the pfet in place, the brewpi will turn off the display after 10 minutes. Tapping the encoder will wake it back up. Without the pfet the display will be always on. It's up to you if that matters.

I h ave a weller soldering station and iit works great. Most of the time I have no issues with soldering. The only issues I've had on this project are the places I have had to try to solder the pfet or wire to existing solder points. Sometimes i end up with too much solder. Really I'm just out of practice.

andrewmalizia · Feb 16, 2015

MrSaLTy said:
Depends... With the pfet in place, the brewpi will turn off the display after 10 minutes. Tapping the encoder will wake it back up. Without the pfet the display will be always on. It's up to you if that matters.

I h ave a weller soldering station and iit works great. Most of the time I have no issues with soldering. The only issues I've had on this project are the places I have had to try to solder the pfet or wire to existing solder points. Sometimes i end up with too much solder. Really I'm just out of practice.

But the screen can be turned off manually with the rotary encoder right?

day_trippr · Feb 16, 2015

andrewmalizia said:
[...]Day_trippr....
Is this the encoder youre using? http://www.amazon.com/dp/B00KHTLWU6/?tag=skimlinks_replacement-20

Yes, I have one of those encoders, as well as a pair of same-but-different-manufacturer switches, running on various minions.
They both work well and have similar tactile characteristics.

Have you done much design of PCBs?

Aside from stints doing chip design and platform architecture, board design has pretty much dominated my 41+ year career.
So, yes, a bit

I'm thinking this would be a pretty simple PCB design since Elco stopped the production. The project could be uploaded to OSHPark and had for about $10/board. I may work up a design if I find some free time.

Please feel free to use anything I've posted on any of the HBT forums, you're more than welcome.
A fully-loaded double-sided Uno R3 shield solution should be a piece of cake.

But if you pay $10 a circuit, make sure you get kissed first

If you get to where you're actually looking for a volume fab shop let me know.
The ~ 1" x 3.5" pcb below is for a 2TB SSD I designed for the current MacBook Pro and is 10 layers, scary tight geometries, controlled impedance, and costs about a buck and a half...

Cheers!

day_trippr · Feb 16, 2015

andrewmalizia said:
But the screen can be turned off manually with the rotary encoder right?

No, that's a function of a 10 minute timer in the Arduino.

So I would say there's no point in installing the backlight control circuit without at least a push-button switch...

Cheers!

andrewmalizia · Feb 16, 2015

day_trippr said:
No, that's a function of a 10 minute timer in the Arduino.

So I would say there's no point in installing the backlight control circuit without at least a push-button switch...

Cheers!

So arduino code shuts down the screen after 10 minutes? And you need the rotary or a switch of sorts to turn the screen back on...

So what is the pfet or the tranny doing in the other design exactly?

andrewmalizia · Feb 16, 2015

day_trippr said:
Yes, I have one of those encoders, as well as a pair of same-but-different-manufacturer switches, running on various minions.
They both work well and have similar tactile characteristics.

Aside from stints doing chip design and platform architecture, board design has pretty much dominated my 41+ year career.
So, yes, a bit

Please feel free to use anything I've posted on any of the HBT forums, you're more than welcome.
A fully-loaded double-sided Uno R3 shield solution should be a piece of cake.

But if you pay $10 a circuit, make sure you get kissed first
If you get to where you're actually looking for a volume fab shop let me know.
The ~ 1" x 3.5" pcb below is for a 2TB SSD I designed for the current MacBook Pro and is 10 layers, scary tight geometries, and costs about a buck and a half...

Cheers!

ummm yeah no thanks! I'm a civil engineer with an interest in electronics and all things fun! haha. That does not look fun. I have a hard enough laying out simple tone circuits for guitar effects I play with. I've mostly resorted to just populating easily purchased fabled PCBs.

day_trippr · Feb 16, 2015

andrewmalizia said:
So arduino code shuts down the screen after 10 minutes? And you need the rotary or a switch of sorts to turn the screen back on...

So what is the pfet or the tranny doing in the other design exactly?

The BrewPi AVR code sets the state of shift register output bit 2 to a "1" after 10 minutes from start up. If you then short UNO digital IO pin D7 to ground, that tells the AVR code to set S/R bit 2 to a "0", which enables the p-fet or the PNP transistor to conduct power through to the LCD back light LEDs, and also restarts the 10 minute timer.

The recommended rotary encoder includes a push button function, but you could substitute a simple push button switch do that much. You'd lose the ability to actually change BrewPi settings without the rotary encoder part, but you'd gain the dimming function...

Cheers!

andrewmalizia · Feb 17, 2015

day_trippr said:
The BrewPi AVR code sets the state of shift register output bit 2 to a "1" after 10 minutes from start up. If you then short UNO digital IO pin D7 to ground, that tells the AVR code to set S/R bit 2 to a "0", which enables the p-fet or the PNP transistor to conduct power through to the LCD back light LEDs, and also restarts the 10 minute timer.

The recommended rotary encoder includes a push button function, but you could substitute a simple push button switch do that much. You'd lose the ability to actually change BrewPi settings without the rotary encoder part, but you'd gain the dimming function...

Cheers!

Hmmm... OK. Maybe I'll add one.

Any suitable tranny subs? I dont have any pfets so far as I know in my arsenal. Most of the trannies i have are npn, plus some irf510 and j201s. I think the only PNP i have are 2n39xx? I dont think i have any 2n7002.

also, is there anything that is worth setting via rotary over web interface? I already have the pi up and running, about to jump out and solder the ic socket for the shift register and some of the wiring

doomy86 · Feb 18, 2015

@andrewmalizia
Just use a 2n3906 like in daytrippers schematic.

I have some problems with both of my brewpi builds, they work ok standalone but with a load connected (aquarium heater) the display gets scrambled after some time (5-10 heating phases).

I suspect there is feedback noise from relay switching, dont have an oscilloscope so i cannot be sure. I have already installed a decoupling capacitor right at the VCC input of the shift register. No change.

My relays have optocouplers, but i dont like the idea of installing a second power source, so i tried feeding the relay directly from the wall wart. No change.

The leads from the arduino to the shift register are already very short ~1cm, from the display to the shift register they are somewhat longer ~15cm.

You can find details of my build here:

https://doomlab.wordpress.com/2015/02/18/brewpi-build/

Any help would be really appreciated.

andrewmalizia · Feb 18, 2015

doomy86 said:
@andrewmalizia
Just use a 2n3906 like in daytrippers schematic.

Somehow looked over that schematic in the middle there. Thanks for making me go back and look for it! haha. I had downloaded the original and it wasnt shown.

day_trippr · Feb 18, 2015

I'm all about change. PKU.

Actually, what happens is the forum won't let me go back and edit posts after some number of days/weeks/I'm not sure what, so I have to keep adding revisions - especially if a chunk of the design hasn't been verified because the parts are on the slowest boat from China ever...

Cheers!

day_trippr · Feb 18, 2015

doomy86 said:
I have some problems with both of my brewpi builds, they work ok standalone but with a load connected (aquarium heater) the display gets scrambled after some time (5-10 heating phases).

I suspect there is feedback noise from relay switching, dont have an oscilloscope so i cannot be sure. I have already installed a decoupling capacitor right at the VCC input of the shift register. No change.

My relays have optocouplers, but i dont like the idea of installing a second power source, so i tried feeding the relay directly from the wall wart. No change.

The leads from the arduino to the shift register are already very short ~1cm, from the display to the shift register they are somewhat longer ~15cm.
[...]

If you disconnect the AC loads on the relays do you still get display errors?
Do you know if your relay modules have snubber diodes across the coils?
Also, what is the actual 5VDC level at the LCD?

btw, at least one other person has gone through this and I believe eventually solved it.
Hopefully he'll chime in...or you could start digging back through the thread...

Cheers!

How To: BrewPi LCD Add-On

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