BrewPi Forum

Goddamnit palitu, you scared me!

I was playing cards with my friends and got a notification e-mail of your message, but could not properly check the files. Pin 9 is not connected to anything, pin 8 is connected to the ground plane.

Hi Elco,

Some small updates, LCD connector pin numbers, moved to bottom for clarity.
Changed 0805 jumpers to solder jumpers from the SparkFun library.

I could swap the molex connectors for flat ones, so they connect to the side, just like the screw terminals.
Goes for the rotary encoder connector as well. Opinions?

Another thing I was wondering: is the turn direction of the contrast pot ok? I have relabeled it constrast btw.

ah those are just rendering issues. Here is a higher resolution:
It still doesn't appear straight, but it is.

well i am excited.  My Leonardo just arrived today (never DX again).  so looking forward to starting up my foray into micro controllers and beer.

I have printed out the layout and checked alignment with some of the components.
Some points of concern:

• The 10 pin connector with lever is huge! It is 2,7 cm high. I can image a lot of people want a lower profile connector to be able to fit this in a box.
• The USB connector of the Arduino Uno is high. It will touch the underside of the PCB at the screw terminals. Arduino Uno users probably need to stack some extra headers in between. I don't see how I can move the screw terminals to prevent this.

@palitu: I stopped ordering for dealextreme a long time ago. You can get the same stuff on eBay and it ships immediately. DX is not what it used to be.

Looks fantastic. I'm most of the way through making my own DIY shield, but I'll definitely get one of these once they're available. I don't suppose you have any idea of what the cost and shipping will be?

I'm all for the lower profile connector without the lever, too. I don't think the added security for the cable is worth the added height or cost. Even if it is only a few cents.

The screw terminals are just an easy, solder free way of connecting things. Could be two pin headers, too, but screw terminals are a bit more sturdy. The SSR's often have kinda big screw clamps, which makes it easier to use a thicker wire. A screw terminal on the board makes that possible.

I could even use mini screw terminals for the temperature sensors, so you don't have to solder a connector to the sensors. These are expensive though and require a mini screw driver.

I will use a red and blue LED.

I have swapped the big connectors for smaller, normal ones. This allowed me to give the JTAG header a bit more space. It also made space for a screw hole on the LCD board.
The screw holes on the LCD board probably will not be used, because it is a backpack, but its nice to have them. The rotary encoder will be mounted through a panel, so it does not need the holes.

Here is the new layout. If I get enough feedback, I could send them to the fab house on Monday.

Elco,
Great work!
a.) LCD module back light current
The spec for my chosen 4x40 blue LCD back light current is:- 150mA max with forward voltage 3.2 volts
For power dissipation reasons change R2 for two 33R 0805 resistors in parallel. (use 1206's if room)
b.) IC1 pull up resistors
Consider adding 10K pull up resistors to the IC1  LCD_CLK  and  LCD_CLK  signal inputs.
This will help with longer 10 way cables. (>1m)
c.) LCD board decoupling caps
1 x 10uF and 2 x 100nF ceramic suggested.

Pleased to see the Q2 and Q3 Fet's are now 2N7002.

By the way, I am also looking into selling complete kits:

This board + LCD + SSR's + cables + DIN connectors + DS18B20 sensors. You just have to get the fridge and thermowell yourself.

Hey Guys,

Hopefully this will be the latest update.

It kept bugging me that the HEAT and COOL outputs did not have a proper ground connection.
I still rather had a GND and 0/5V pin, so I decided last minute to change circuit to a P-Channel MOSFET equivalent.

The open drain setup with NFET's wasn't really suitable for use with higher voltages, because when you are not using the 5V line, what is your reference voltage?

This P-Channel MOSFET setup is easier to understand and can source 180mA at 5V. So it is able to drive relays and can be used as a true digital output. If you want to use actuators with a higher voltage, just add a transistor circuit yourself after these outputs, using GND as a reference.

I changed the backlight setup to use the same P-Channel MOSFET. Any comments on the resistance for the backlight?





Holes at the top are to align the solder paste stencil.

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Hi Elco,
1.) I would have kept Q4 and Q5 as 2N7002, but no real objection to
you using the P-Channel BSS84 Fets. (I will use SSR's)
Are pull up resistors required on the Gate pins of Q4 and Q5? During
Power On Reset (Or Reset) of the Arduino Leonardo ATmega32U4 the PC6 and
PD7 pins (Or Uno ATmega328P PD5 and PD6) go tri-state, according to the
data sheet. Without pull ups Q4 and Q5 might randomly turn on during a
processor reset. Not ideal. I have not previously used ATmega processors
before - so this may not be an issue.
2.) I will probably change the values of R4 and R5 to suit the chosen
LCD display optimum back light level. 33R just seemed a good 'middle of
the road' starting value.

3.) Decoupling Caps. Yes your choice of decoupling caps look OK.
4.) R14 value. Changing R14 to 4K7 is a good idea. Making R14 1K - better still?
I hope this helps.

@JohnCass
1. With the current layout it is possible to connect a 6 strand cable to the connectors. This is easier to use and to understand for most people I think. You can have just one ground wire, which you split when in the fridge, but for most people this will only make it harder.

2. This is also something that would not be used that much probably.
To keep SPI usable, I would only have to relocate pin 10. A SPI device only communicates when SS is active. But there are no pins to move to, while maintaining compatibility with both the UNO and the Leonardo. 1-2: keep free on the UNO to not mess with serial communication, 2: SDA on the Leonardo. A0-A3: JTAG on the Leonardo.
The best candidate would be 2, so I would have to swap 10 and 2. This would free the default SS pin. I used it because it makes sense to use it, but so does everybody else.

@Georgech1
1. If there is room, I'll add them. Especially with the Leonardo, which is in bootload mode for 6 seconds, it makes sense.
2. Ok, I'll play it safe and use 33. The visible difference between 100 and 150 will be small.
4. With 4K7 the current will be 1mA. I think increasing it further is not needed. Some fridge door switches conduct when the door is closed, so this current will flow continuously.

@palitu
I want to order the boards this week, but I am going snowboarding in 12 days. I don't think it is realistic to promise assembled boards before Christmas. But I think the first week of January I can ship them.

Hey Elco, 

How about a nice hoppy green??

Elco,

Looks good man. I don't think you really needed to switch over to P-Channel FET's but it matters not to me as I'll be using SSR's that really don't care that much about the drive voltage and such, it'll work fine either way.

An idea I was kicking around was maybe you could put a pattern within the pattern of the screw terminals that allows for those lower profile right angle connectors. I do that a lot in layouts, co-location of alternate component styles. I also do things with build options like putting parts under parts such that it's physically impossible to co-mingle build options. For instance if you're say bypassing some buffers you put the zero ohm resistors under the package of the buffer on the same side such that the two can never be installed at the same time, i.e. a weird illegal configuration. I've worked at a fair number of places that did small hand stuffed run, obviously with PnP machines such things aren't a valid concern.

Anyhow the reason I bring up low profile is because I'm contemplating putting the SSR's, bulky outlets and power cords etc into a remote power box to sit on the floor behind the freezer. The display, RPi, Arduino and all of that will go inside of either a pre-bought deep picture frame or one that I make myself. The two boxes will just attach through an umbilical cord.

The benefit is this. I think all the high power electronics should be in a durable flame proof enclosure for safety reasons and so that the housing can be properly grounded. That isn't terribly compatible with for instance having a WiFi dongle in there. So stuffing it all into a picture frame type thing gets me a few things. The frame can be wood which is RF friendly relatively speaking. The front, "glass" can be Perspex/Acrylic which we can all handle cutting cleanly enough to look nice in a frame. Finally making your own bezel for a display is hard. I own a professional Mat cutter for framing pics which means I can make a very nice, closely trimmed opening in a good looking mat to have the display peek through. The front, "glass" being acrylic the encoder can come through easily...it's too hard to drill glass reliably.

The lower the profile of the connectors the less deep this whole frame needs to be!

How much do you expect you're going to want for the boards?

Regards,

James

Will you be making the eagle files public? :)

/Carl

Elco,

All I meant is you could put inside of the Cool, Heat and Door patterns provisions for connectors more like the Onewire1 and 2 connectors but in 2 pin versions. If someone buys the shield unpopulated they can just solder in whichever type of connector they prefer. Possibly the screw terminals aren't substantially taller than the right angle molex? If that's the case it's all moot really...

I would be careful of the constantly moving goal posts, I think this is a really solid first pass...gets some boards printed and expand the base! Honestly I think your project deserves way more focus than it's getting now, the sooner the whole thing is more plug and play the sooner less techy types of people can start adopting this system. Having to assemble ones own shield may be too much for some, having turn-key pre-assembled ones is a good idea.

Regards,

James R.

Elco, with all your work on this project - don't make the eagle free: you deserve to make a few bucks off these boards.  i am donating  what I can tonight, and will buy you plenty more beers in the future. when you get these made I will defiantly buy one !!!

@Elco - would a 6 pin socket fit across both 3 pin headers for the sensors? (looks like spacing between them is slightly > 2.54mm) - this would help for putting both sensors onto a single cable for taking into the fridge.

I wonder if one could fit 2x small 5v relays on the prototyping pads area....

great elco, cant wait to see the boards for real!

Just in time before my snowboarding holiday: check out the blog for pictures of the new PCB's!