Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 21 of 21

Thread: ToZero: A Teensy to Pi Zero form-factor adapter

  1. #1

    ToZero: A Teensy to Pi Zero form-factor adapter

    Hi All,

    I wanted to share with and get people's thoughts on a board I've been working on over the summer. Called the ToZero, it's an adapter (well two) for the Teensy 3x and 4x to the Raspberry Pi Zero form-factor, letting people use Pi HATs with their teensy.

    Click image for larger version. 

Name:	tozeros+teensys.jpg 
Views:	32 
Size:	93.1 KB 
ID:	21851 Click image for larger version. 

Name:	tozeros_noteensy.jpg 
Views:	33 
Size:	390.0 KB 
ID:	21852 Click image for larger version. 

Name:	ToZero+41.jpg 
Views:	31 
Size:	166.4 KB 
ID:	21853 Click image for larger version. 

Name:	ToZero+Unicorn.jpg 
Views:	25 
Size:	101.8 KB 
ID:	21854
    WIP Documentation: http://zodiusinfuser.uk/products/tozero/
    Demo Tweets:


    It came about because I love all the Pi HATs that are out there but have yet to really get into the Raspberry Pi itself. Being a regular user of the Teensy for other projects, I saw that it's small size would fit into a Zero form factor so decided to make this adapter that married the two.
    It's similar in this respects to the Arduino and Feather adapters by Sparkfun and Adafruit, respectively (https://www.sparkfun.com/products/15716, https://www.adafruit.com/product/3200)

    Reason I am posting this here rather than in the projects / blog section, is because I am both curious whether this is something people would actually be interested in as a product, and whether there are any revisions I should consider from those with more Teensy experience than I before making more or outsourcing production. I have only made around 10 so far, a few for myself and the rest for alpha testers, and the only hardware issue that has come back is with the power multiplexer IC, which I need to switch SKU to fix.

    Thanks for your time

  2. #2
    Senior Member+ KurtE's Avatar
    Join Date
    Jan 2014
    Posts
    7,901
    Looks like fun. I have done some larger hats for other RPI boards, but not for the Pi zero...

    Could be an interesting product.

  3. #3
    Senior Member
    Join Date
    May 2015
    Location
    USA
    Posts
    717
    Nice, I see it also has a power supply.

  4. #4
    Senior Member
    Join Date
    Jul 2020
    Posts
    174
    Interesting project.

    I notice the "$5" Pi Zero is still never actually $5, or anywhere close to it, years after its release. That's too bad.

  5. #5
    Quote Originally Posted by KurtE View Post
    Could be an interesting product.
    Quote Originally Posted by Pilot View Post
    Interesting project.
    Thanks!

    Quote Originally Posted by jonr View Post
    Nice, I see it also has a power supply.
    Yes, it has space for a 5V screw terminal input either above or below in addition to the onboard USB port.

    I would say the main feature of the board, other than the GPIO mapping itself, is the power multiplexer IC. This allows both the Teensy USB and an external source to be connected simultaneously, letting people drive high current HATs (usually LED based) without drawing 2A from a PC's USB port (or triggering the fuse on the Teensy 3x). This was an issue I personally experienced with the very first prototype. The chip I have gone for also has the advantage that it does seamless switchover, letting you occasionally plug a portable project into USB from time to time to send config commands without rebooting.

    Other features of the board include:
    • Headers for Teensy-only functions (e.g. ADCs, DACs, CAN Bus, S/PDIF, On/Off)
    • Headers for secondary I2C and SPI channels that match the Pimoroni breakout garden pinout
    • A dedicated 600mA 3.3V regulator for Pi HATs that supports the Teensy 4's on/off feature
    • 3V Real-time Clock (RTC) battery connector
    • I2C Pull-up resistors pre-installed


    I did consider adding power regulation / battery management at one point, but they seemed beyond the scope of what was originally intended as a simple adapter. Also, for a 2 layer board, the routing on both these adapters is quite dense

  6. #6
    Senior Member+ MichaelMeissner's Avatar
    Join Date
    Nov 2012
    Location
    Ayer Massachussetts
    Posts
    3,881
    Quote Originally Posted by Pilot View Post
    Interesting project.

    I notice the "$5" Pi Zero is still never actually $5, or anywhere close to it, years after its release. That's too bad.
    It depends on where/when you buy it, and whether you are just buying the pi zero alone, or with other things to cover the cost of shipping.

    The US chain Microcenter, no longer sells the plain Zero, but it does sell the Zero-W for $10, which is its stated price. I do think I bought at least one Zero from Microcenter retail. Of course, I had to add the $0.33 tax. Now, Microcenter will charge the $5/10 sticker price if you are buying just one, but if you are buying multiple Pi's, then the price goes up. However, that only helps if you live in a place that has a Microcenter.

    Adafruit does sell the Zero-W for $10 and the plain Zero them for $5. You can only buy one at a time, and of course shipping is not free at Adafruit. In fact, I went to buy something there recently, and I saw the UPS or Fedex ground shipping had gone up from the last time I ordered at Adafruit.

    Back when I was still interested in Pi's, I think I remember reading an article, where the Pi Zero actually was more than $5 to make, and the Pi Foundation would do a run on Pi's Zeros after doing Pi Threes (or now Pi Fours) to pay the bills and make a few Pi Zero's afterwards. You don't see most of the commercial sites carrying the Pi Zero's because there is no margin. Places like Adafruit sell it as a loss leader, with the hopes that they will make up for it in other sales.

    Given the Pi Foundation primarily wants people to code, the Zero is an effective wedge to get people going (assuming you have a display and SD card). I tend to think of it as a hobby project, and not one designed to make money. The trouble is shortly after the Pi Zero came out, the bitcoin miners discovered it, and often times pushed out the proto-hackers that were its intended market.

  7. #7
    Senior Member
    Join Date
    May 2015
    Location
    USA
    Posts
    717
    So if I connect the teensy to a USB-C port, then there is at least .6A available for HATs and .3A for the teensy? With no need to cut the jumper on the teensy?

  8. #8
    Senior Member+ MichaelMeissner's Avatar
    Join Date
    Nov 2012
    Location
    Ayer Massachussetts
    Posts
    3,881
    Quote Originally Posted by jonr View Post
    So if I connect the teensy to a USB-C port, then there is at least .6A available for HATs and .3A for the teensy? With no need to cut the jumper on the teensy?
    Ummm, the Teensy has a USB micro-B port, not a USB-C port. Similarly, the Pi Zero and Pi Zero-W were powered with USB micro-B.

    Running blink, I get about 70mA on the Teensy 3.6 and perhaps 100mA on the Teensy 4.0. Note, this was running default code. You can always run it in lower power modes.

    If you never have two power sources, you don't have to cut the jumper. Which ever power source is connected will power the whole thing. With an external board, you could what the Teensy -> Feather adapter does. If there is power from the Teensy, the Feather adapter does not feed its battery power back to VIN (and it can use the power to charge the battery). If VIN doesn't have power, then the adapter feeds the power into VIN.

    Where you want to cut the jumper is if you want to program the Teensy via external USB, but you need to have an independent power source to power the rig (for example, you need more power than you can typically get with USB micro-B, or if you are running motors or servos, they likely need more power). An alternative to cutting the jumper pad is make up a USB cable that provides the data pins, but not the power. Then the Teensy will get the power from the external source.

    In general, if you are plugging into a random USB source, 500mA (at 5v) is about the most you will typically get. IIRC, that is what the USB 2.1 standard specifies. The Teensy does not do any power management, so it depends on what your computer, battery, or A/C converter provides. I do have batteries and A/C converters that explicitly are not 'smart' and always deliver around 2.1 amps of power. But most things are geared towards cell phones, and will only give the power requested. This means if you need a lot of juice, you have to pay attention when using a power supply.

  9. #9
    Senior Member
    Join Date
    May 2015
    Location
    USA
    Posts
    717
    Whoops, I meant USB 3.0 port (on the PC end), not USB-C.

  10. #10
    Senior Member
    Join Date
    Jul 2020
    Posts
    174
    Is there a not too difficult way power could come from USB, or the other input if available, with automatic switching (like with a transistor) instead of cutting a trace?

  11. #11
    Quote Originally Posted by Pilot View Post
    Is there a not too difficult way power could come from USB, or the other input if available, with automatic switching (like with a transistor) instead of cutting a trace?
    Are you asking for the ToZero or just in general? Because with the ToZero you do get automatic switching, but you need to cut the trace and solder on the VUSB pin for it to work. If you don't do that then you can still use either power input, just not simultaneously.

  12. #12
    Senior Member
    Join Date
    Jul 2020
    Posts
    174
    I mean for the ToZero.

  13. #13
    Quote Originally Posted by Pilot View Post
    I mean for the ToZero.
    In that case, the answer to your question is no, the trace needs to be cut if you want auto-switching. This is because the VIN pin is both an input and an output. When plugged into USB it outputs 5V to your circuit, and when you want to power the Teensy off a separate source you feed 5V into that pin. This bi-directional nature of the pin presents a problem for power sharing, but can be solved by cutting the trace to disconnect VUSB from VIN, thereby turning VIN into an input only which is much easier to deal with.

  14. #14
    Senior Member
    Join Date
    Mar 2016
    Posts
    242
    This looks well thought out. Good job.

    What power multiplexer are you using? I've been looking at the TPS2114/5 for a project I'm doing and have exactly the same problem of the bidirectional power pin. I thought about just using a MOSFET but recognize a few more smarts are needed.

  15. #15
    Senior Member
    Join Date
    Mar 2016
    Posts
    242
    On your original question - is there a market for these? Definitely. You've done a lot of the hard work (including documentation!) so might as well harvest a little reward for it. Tindie is an easy way to do this though they do take their cut. I'd do an initial batch of 20 or 30 to test the demand. If you post updates and "how to" articles in the obvious places you can increase the interest. I wouldn't surprised if you sold several hundred over the course of a few months. You won't get rich but it's a great way to fund your hobby. Plus, having customers is a great way to see how people are using it and will give you ideas for follow on projects/products. It makes you a better engineer/designer/...

    Probably your biggest question is pricing it. It's yours to decide but I wouldn't price it below $10 or above $20. Maybe sell it in 2 or 3 packs since processing orders takes time. 1 for $20, 3 for $30? (to encourage multiples) Of course substitute pounds or euros for $.

  16. #16
    Quote Originally Posted by PhilB View Post
    This looks well thought out. Good job.
    Thanks! It took a while to develop the two boards (T3 and T4 variants), not to mention the very first prototype I made over a year ago that had no SMD components on.

    What power multiplexer are you using? I've been looking at the TPS2114/5 for a project I'm doing and have exactly the same problem of the bidirectional power pin. I thought about just using a MOSFET but recognize a few more smarts are needed.
    I'm using the TPS2115, but will be swapping to the 2113 in the next revision. I found that for automatic switching based on the presence of a primary input, the 2114 switched to it fine but when switching back would take a good few seconds resulting in an MCU reboot from the output voltage dropping. This seems to be caused by the internal current source on its D pins, causing the line to hover around 2V when the input is removed. Even with a low value pull-down I couldn't get rid of the problem.
    The 2113 on the other hand lets you use a voltage divider to specify the voltage the primary input needs to reach before it will be switched to. Texas actually acknowledge that the 2113 is the intended chip for this purpose, but only discovered this after developing the board: https://e2e.ti.com/support/power-man...match=TPS2115A

    Pololu sell a breakout if you want to try the 2113 for your use-case: https://www.pololu.com/product/2596


    Quote Originally Posted by PhilB View Post
    On your original question - is there a market for these? Definitely. You've done a lot of the hard work (including documentation!) so might as well harvest a little reward for it. Tindie is an easy way to do this though they do take their cut. I'd do an initial batch of 20 or 30 to test the demand. If you post updates and "how to" articles in the obvious places you can increase the interest. I wouldn't surprised if you sold several hundred over the course of a few months. You won't get rich but it's a great way to fund your hobby. Plus, having customers is a great way to see how people are using it and will give you ideas for follow on projects/products. It makes you a better engineer/designer/...
    Thanks for the encouragement! What you describe would be the ideal outcome from this project

    Going the Tindie route does appeal, and I've heard good things from other sellers about it. You may have to enlighten me on what those "obvious places" are, as the only one I really know of is Hackaday.io.

    Since posting this thread I came across a similar project, called the ATMegaZero (https://groupgets.com/campaigns/822-atmegazero), that seems to have a bit of buzz around it for being a Pi Zero form-factor Arduino. The current version does have some limitations (5V logic for instance) but hopefully the ToZero will appeal to the same audience.

    Probably your biggest question is pricing it. It's yours to decide but I wouldn't price it below $10 or above $20. Maybe sell it in 2 or 3 packs since processing orders takes time. 1 for $20, 3 for $30? (to encourage multiples) Of course substitute pounds or euros for $.
    I was thinking around the $10 mark, but hadn't considered the multi-pack option! Price would also depend on if headers are included or not, which I can see being an attractive option for some people.

  17. #17
    Senior Member
    Join Date
    Mar 2016
    Posts
    242
    Thanks. I'll look at the 2113. My Chinese assembler has them in stock so it would be easy.

    $10 may be a reasonable price for 1 but you should factor in your time to package and ship. Consider your net per transaction. At $10/transaction, you have to work a certain amount. At $20, you work half that for about the same net. And make no mistake about it - each transaction is a distraction from other things (unless you live to sell stuff!).

    Usual places would be forums like PJRC, PI forums, electronics forums. Then there are places where people might use your product to do something - maybe IOT type stuff. You would best be served by creating some projects that use your board - LED based stuff is obvious but I'm sure there are others. When people see a project that uses your board they will order one (or 3). Encourage your customers to post about their projects, too.

  18. #18
    Senior Member
    Join Date
    Jul 2020
    Posts
    174
    Also factor in the cost of servicing RMAs (either because the board is defective, or because the customer bit off more than they could chew), having to provide tech support, maintaining ongoing relations with customers, handling customers who aren't mentally in the right place to work with this and project their frustration incorrectly onto you (which you will have to endure sooner or later), etc, etc, etc...

    Consider the price at which all of that is worth the trouble, and don't charge less than that unless you're hard up.

  19. #19
    Senior Member
    Join Date
    Mar 2016
    Posts
    242
    Yeah, all those can add up. I've seen it all except for returns. Haven't had one yet though I expect it to happen. I do a visual inspection on everything I ship so at least obvious stuff gets caught. And, I use my own products so I know that they are going through. You can get needy customers but even those give you insight to how your product is perceived and is an opportunity to make your product, documentation, etc better. In general, if you treat them with respect and take their issues seriously, they won't dump on you.

  20. #20
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    Posts
    12,685
    Cool project and possibilites.

    Maybe some of that is why TallDog/loglow on Tindie posts a discount coupon for Forum users.

  21. #21
    Member
    Join Date
    Feb 2020
    Location
    South Africa
    Posts
    41
    You say on your Github page: "It also includes a number of example sketches for driving Raspberry Pi HATs (this will be expanded upon over time)."

    That is one of the most important things to add: start a database of Pi HATs and their (modified?) drivers that are compatible with your expansion board and the Teensy.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •