Ultimate Kitchen Timer

[caswal]

Hi all,

I've been wanting to make the leap from designing some simple PCB logic/connector boards for my Arduino based projects. To making PCBs with the MCU integrated.

While cooking dinner the other night, I wanted to quickly keep time of a couple of things. I ended up using my phone. I guess I could get a google home or something. But I thought it would be cool to have a digital kitchen timer with a rotary encoder to roll on time. Have that nice satisfying tactile feedback and also doesn't matter too much if your hands are covered in something.

I then thought about why not 4 Timers with 4 Encoders? When not in use it could display the Date, Time, Temp and something else. I think I could get quite a cool aesthetic look, with a knob on each corner, and 4 separate OLED displays.

My learning goals for this are:

• Learn to AVR MCU Integrated into the PCB
• Learn how to flash it with ISP
• Learn charge control and protection of Li-Ion batteries
• Learn EasyEDA and see what its integration with JLC PCB is like

So my design requirements for the timer are

• 4 Cheap Aliexpress OLED Displays
• 4 Rotary Encoders
• Micro USB recharging
• Charge control and protection of Lion Battery
• Date, Time, Temp and Humidy display when not in use
• And I almost forgot, make sound when finished

My Equipment on hand:

• Large Format 3D FDM Printer
• Fine detail FDM Printer
• CNC Router
• DS1052 Scope, Multimeters, Bench Power supply
• Soldering and rework station.

This is my schematic, and beginnings of some board layout here: https://easyeda.com/caswal/kitchentimer

I would love some feedback on the schematic, as I really feel like I don't know what I am doing.

Thanks for any help.

[sokoloff]

Free thoughts (double your money back if not satisfied):

You might consider an ESP(8266 or 32, though 8266 is "plenty" for this app) if you have any idea that this might end up with an Alexa/Home or phone integration down the line.
It's another buck or two in BOM cost at most but gets you WiFi connectivity.

I might also go for a single, larger display which will probably look more "finished/right" than trying to get 4 separate displays to look good.

Use a PCB for the outer panel as a cheap and fast way to get a good looking panel with good dimensions and labels.

There are rotary encoders with nice feeling detents if that's important to you.

But honestly, even since we got our Alexa Show that's been the kitchen timer of choice for us. (You talk about having your hands gross or tied up. That's totally true, which makes voice control a killer feature IMO.)

[IamSynthetiC]

Right away i can see you have no oscillator for your arduino. I suggest looking at the official Arduino website for the schematics of an arduino Uno (whitch uses the Atmega328P-PU) and copying as much as possible.
https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf
You will also need a programmer (externall, onboard, or another arduino) (the programmer is included on the above schematic).
GreatScott has made a very nice video about Standalone Arduino Circuits where he explains how to build one, and how to program it. 


As far as the battery goes, i am no expert. In my experience however Li-po batteries are easier to work with. (18650 batteries are a prime example)
They have a plethora of BMS modules you can choose from, and are incorporated into many designs which you can find and follow.
GreatScott has again two videos regarding BMSs that are both great. (spoiler : dont build one, buy one)

Also i see no power supply in your design. You should use an SMPS (No Post-SMPS LDO required) aimed toward battery-powered applications, they are not hard to find. The topology of the SMPS is dependent on your battery's voltage.


I do not see any other problem at this time. Overall your idea is sound. But in my experience the procces of integrating arduino modules on a single PCB is not always cost effective . I would personally buy the external modules, put them all together, and then hide as much as possible in a box. But this is your choice. Regardless your idea is great, and i might even follow it in the future with some spare nixie tubes i have lying around.

Good luck in your efforts.

[caswal]

Free thoughts (double your money back if not satisfied):

You might consider an ESP(8266 or 32, though 8266 is "plenty" for this app) if you have any idea that this might end up with an Alexa/Home or phone integration down the line.
It's another buck or two in BOM cost at most but gets you WiFi connectivity.

I might also go for a single, larger display which will probably look more "finished/right" than trying to get 4 separate displays to look good.

Use a PCB for the outer panel as a cheap and fast way to get a good looking panel with good dimensions and labels.

There are rotary encoders with nice feeling detents if that's important to you.

But honestly, even since we got our Alexa Show that's been the kitchen timer of choice for us. (You talk about having your hands gross or tied up. That's totally true, which makes voice control a killer feature IMO.)

I have used ESP's for things before, but this project was about playing with Atmel/AVR's. I plan to also use this as my first foray into Atmel Studio. I could always add an ESP extension via the UART in the future.

The 4 separate displays are a part of my design language, of having the timer display physically tied to the encoder.

I did do a bit of search for a rotary encoder, and found some 24 Step encoders for musical instruments. I assume it will have pretty good feel.

Right away i can see you have no oscillator for your arduino. I suggest looking at the official Arduino website for the schematics of an arduino Uno (whitch uses the Atmega328P-PU) and copying as much as possible.
https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf
You will also need a programmer (externall, onboard, or another arduino) (the programmer is included on the above schematic).
GreatScott has made a very nice video about Standalone Arduino Circuits where he explains how to build one, and how to program it. 


As far as the battery goes, i am no expert. In my experience however Li-po batteries are easier to work with. (18650 batteries are a prime example)
They have a plethora of BMS modules you can choose from, and are incorporated into many designs which you can find and follow.
GreatScott has again two videos regarding BMSs that are both great. (spoiler : dont build one, buy one)

Also i see no power supply in your design. You should use an SMPS (No Post-SMPS LDO required) aimed toward battery-powered applications, they are not hard to find. The topology of the SMPS is dependent on your battery's voltage.


I do not see any other problem at this time. Overall your idea is sound. But in my experience the procces of integrating arduino modules on a single PCB is not always cost effective . I would personally buy the external modules, put them all together, and then hide as much as possible in a box. But this is your choice. Regardless your idea is great, and i might even follow it in the future with some spare nixie tubes i have lying around.

Good luck in your efforts.

The 328p has an internal 8mhz oscillator. This is supported by the Arduino IDE, with an extra board configuration. Is described here: https://www.arduino.cc/en/Tutorial/ArduinoToBreadboard
Although I plan for this to also be my first  Atmel Studio project.

Using the External RTC I'm not too fussed by the timing fluctuations of the internal oscillator. So don't need the stability of the external clock.

I have a SMPS on the Battery/Power Sheet producing 5V?

Another learning reason for this project, is that I am helping a friend build an EV Hillclimb race car. I want to adapt the diyBMS v4 by Stuart Pittaway to make custom modules for the batteries we want to use. It is based around the ATTiny841. Hence the specific AVR focus. Although this has no relation battery management circuitry of this project. We will need to get around 50 balance boards produced.

Thanks for the feedback so far. Is appreciated.

[caswal]

A few updates, like adding a reset button. Working on the layout,

I just need some help confirming I have got this right. I did look over the Schemtic IamSynthetiC linked. And that gave me the idea that it might be nice to run this just off USB. Which it could not due to the +5V rail is from the boost controller that sources from the battery.

So I think I have successfully adapted the Arduino's USB/VIN Selection, of a P Channel Mosfet and Op Amp to do the same trick. To close togther the USB +5V and Boost Converter's +5V line when USB is plugged in. But Block the Boost Conveter's +5V Output from running back into the charge controller, not not attempting to charge itself. Schematic Here, Battery/Power Sheet: https://easyeda.com/caswal/kitchentimer

[ledtester]

Working in the kitchen can get messy. May I suggest using some touch sensors - i.e. something like the TTP223. You can find these ready to use modules on amazon/ebay/aliexpress for cheap:

https://uge-one.com/image/cache/catalog/001/TTP223-Touch-Button-Module-600x315w.jpg

That way you can be holding a bowl with one hand, a spatula with the other and still manipulate the timer with your pinky.

Also, they don't have to be exposed to work. You can place the them in an enclosure (right up against the top surface) and they'll still work.

[IamSynthetiC]

I have a SMPS on the Battery/Power Sheet producing 5V?

I didnt know i could scroll down  .

I had a closer look of your schematics and layout, and it all seems fine.
if you are planning on running this allong with usb power, it may be best not to block the Boost converter but to outright disable it ,if there is such an option (to save some battery).

*Edit : On Q4 pin 6 labeled S2, it seems to be connected right, but idealy there should be 2 dots. EasyEDA is inconsistent, so you sould check the connection regardless.(on the PCB it is right)

[caswal]

Working in the kitchen can get messy. May I suggest using some touch sensors - i.e. something like the TTP223. You can find these ready to use modules on amazon/ebay/aliexpress for cheap:

https://uge-one.com/image/cache/catalog/001/TTP223-Touch-Button-Module-600x315w.jpg

That way you can be holding a bowl with one hand, a spatula with the other and still manipulate the timer with your pinky.

Also, they don't have to be exposed to work. You can place the them in an enclosure (right up against the top surface) and they'll still work.

All depends what we want in the kitchen timer. I just imagine having a finger covered in something wet, leaving that on the capacitive button and sending in bonkers.

I have a SMPS on the Battery/Power Sheet producing 5V?

*Edit : On Q4 pin 6 labeled S2, it seems to be connected right, but idealy there should be 2 dots. EasyEDA is inconsistent, so you sould check the connection regardless.(on the PCB it is right)

Appears to have run the wire behind the other and linked to the Dot next to pin 7. Fixed. Thanks.

[Sampea]

hmm, I had some problems with my kitchen timer but they all seem to have gone away now... on their own. I don't really understand the technical part of all this stuff but I really love designing the kitchen. I don't know why, but it brings me so much joy when I design a kitchen and each time it is different. I came across this cabinetselect.com not so long ago when I was searching for ideas for our kitchen and found great samples there! As a designer I have found it rather inspiring and useful. If anyone needs help, you can write me in pm