If you are reading this - thank you! (if I by posting this break any rules in this forum then I'm sorry in advance. I read the FAQ and tried to comply as much as I could)
Below is a long text describing what I intend to do and in order to get the best help I've tried to describe the project as much in detail as I can. I think I know my way around Eagle now on a basic level but I'm still crawling with regards to my skills in electronics design, but I try to learn.
I've posted a link to the board and schematic files made in Eagle 6.4 in the end of this post.
Timstock Light - What is it and the background:
This is a device for autistic kids in order to visualize time connected to tasks in real life.
The buttons are from left 5, 10, 15 and 20 minutes and they each start a countdown which is visible by leds turning off from right to left.
When a countdown has started it is only possible to cancel it by pressing button 2+4 for 5 seconds but this is not demonstrated to the users. (autistic people can cheat too
)
The reason for keeping it as slim as possible is to be able to stick it inside a folder next to a list of activities that needs to be done. Each activity has a value (time+colour) that tells the user how long time he/she should spend on the activity. (this methodology is already used globally) Some users have it on their desk, in the pocket, inside the desk and so on...
It is technically not more complicated than your average arduino blinky button starter kit, but for some it will be very important and should never fail.
It should also be as simple as possible with regards to components and their costs. The commercially available tools like this today are really bulky, heavy and VERY expensive. This is a low-cost alternative that I will release as open source as soon as I have a verified prototype.
I have also thought about robustness and I don't want components to be easily ripped off... (hence why the buttons are thru-hole in my design since I guess they are more sturdy.)
If it's not too expensive I might get a plastic film printed that'll protect the PCB and components on the front but the goal is to keep costs at reasonable level without going crazy. I can't estimate if 100 of these will be built or 100'000 so the design is for fewer and to be hand assembled for now. (older autistic kids can even do it as a kit!)
I am doing this project since many kids and schools simply can't afford to give these tools to kids who need them and the goal is to make it so cheap they can just hand them out to whoever need one. Parents should be able to buy them for their autistic kids without getting ruined and those who are able to build his/her own hardware (or variant) should be able to do so - as long as they don't sell it for a profit! (I will sell it for whatever they cost me to make and I will not take any profit from it. If someone wants to donate for future work then that's ok.)
I've contacted the original designer and I'm allowed to do this and I did a software only (Android) version more than two years ago which recycles old phones into tools instead - available for free. This is very popular but phones are bulky and this is where this project started.
Usage:
Device waits for input from either of the four buttons and starts a countdown when a button is pressed.
The countdown is visualized with the leds and will counted down to 0. (all leds are lit when started and one by one is turned off to represent accurate time that passes)
The countdown will be possible to reset by pressing two buttons (2 and 4) for 5 seconds.
The board is powered by 3v battery on the back.
When not in use it will run in power consumption mode. (a power switch will reset the counter hence why it's not in the design)
Design:
The reason for using ws2812b is both less components and customization possibilities. (+future features) According to spec 3v should be enough to drive the leds and less bright would be better but this I have to test before I know if it's the right way to go. I have used this led before and it's so simple to use - just wire up as many as you want and have power for!
ISP header mounted on the back for both programming and debug features during development. Will not populate on finished product but want the ability for now.
Will ISP header work with current pin-usage on the attiny85?
Is it necessary with one 15pf cap per led or can this be done with one cap with different/same value on a common vcc "rail" to the leds? (took the layout from ws2812b documentation) It is just a cap between gnd and vcc where led led is powered and although schematic seems logical, reality is really just a bunch of caps between gnd and vcc towards the leds.
I have no formal training in electronics design but I'm a tinkerer at home and try to learn new things in life. I have made a few pcb's in the past and I've made the same mistakes as anyone else but since this project is purely financed out of my pocket I hope someone could be kind enough to review my design in order to get something early that actually work as intended when the components are soldered in place. I can't go through too many iterations before I have something I can give the kids.
I have not done anything with the silk screen stuff yet so text etc are in wrong places.
Everything apart from leds and the four buttons can be moved around but I prefer to have the battery centered on the backside and slightly towards the top in case someone want to put it on a desk or table.
I prefer to stick with the attiny85 since I'm rather used to writing code for those microcontrollers and I've never worked with PIC, but if you think this solution is foobar then change I will.
I'd love to receive feedback for the design and suggestions for improvements. I know my skill is on beginner-tinkerer level, hence why I ask for help.
Perhaps my design needs drastic changes, then please feel free to implement them. I'll include the name(s) on the board of people who aided in the design!
Making something quickly at home on protoboard is one thing, making something for the public is way different and here I simply lack the skill.
Routing is something I still struggle with and watching Dave do it makes me wanna forget everything I know and stick to writing code - but I try as best I can. Sadly have none to talk to locally since I work only with software and they don't really talk hardware at all
Why am I doing this? I have two autistic boys and every little piece of electronic gadget that can help them costs stupid money! (one small whyteboard with leds and a digital clock I got the a few years ago - $1200!!!)
I've written tons of software to help them throughout the years and if I do something that I think is useful for others I put in the hours and release them for free. I've done a few hardware projects on protoboard but this needs to be for real and I don't want to give up due to my incompetence and too much time spent doing the wrong things...
Here is the zipfile containing board and schematic.
http://arrendegarden.se/bilder/TimstockSlim.zipTL;DR
I need help with review (or redesign) of a board I've designed for autistic kids. It's a visual aid for showing time counting down from 5, 10, 15 or 20 minutes to 0.
It will be released as an Open Source project and sold as non-profit in order to make it available to those who might not afford what's available on the market today.
I'm a PCB and electronics noob but I want to become better.
Many thanks in advance! I hope my lengthy description didn't ruin my chances but this is an important tool for thousands of kids and adults today and I want more to be able to get it!
Jens, bearded Swede