thunderbolt with 5 teensies

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kteepa

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I've been doing some reading about how to connect a bunch of teensies together, but the forum posts I've found have either been for different devices or very outdated based on the use of old USB technology.

I have a macbook pro 2019 16 inch, which has 4 thunderbolt 3 ports. As far as I can tell, these ports support 15V at 5W for a total of 3amps each.

I have a teensy 4.1 with a bunch of different types of sensors attached with its own dedicated thunderbolt port on the macbook pro. I would also like to leave 1 thunderbolt port empty. This leaves 2 available thunderbolt ports.


Goal: power 5 more teensy 4.1s through the same macbook pro. Each of these teensies would be exclusively dedicated to reading a single capacitive proximity sensor and sending the output to the main teensy 4.1 (above).

I would like to achieve this by powering these teensies with a single thunderbolt port if possible, otherwise 2 ports is okay. None of the teensies would be overclocked, so they'd be running around 100mA. They do not need to be able to serially communicate with the laptop, just need power.

Would any of these options work? (ranked in order of my preference)
1) plugging in 1 of the 5 teensies to the laptop thunderbolt port, then connecting the daisy chaining the remaining 4 teensies in series by plugging in the Vin and GND of the 2nd teensy to the 1st, of the 3rd teensy to the 2nd, and so on. My concern is this would surpass the max current that can be handled by teensy 4.1
2) plugging in a usb hub (something like the TP-LINK 7 port UH720 Hub 7 x SuperSpeed USB 3.0 desktop) to the thunderbolt port on the macbook and plugging in each of the 5 teensies individually through their own usb cables to the hub. Critically, I do not want to use a powered hub, only something that draws power just from the macbook pro.
3) Using a nonpowered hub for each of two thunderbolt ports and plugging in 3 teensies to one and 2 teensies to the other.

If none of these options work, would I be able to make one of them work if I used teensy 3.2s instead? (draw max 50mA each)

Thanks!




Goal: power 5 more teensies (either 5 teensy 4.1s or 5 teensy 3.2s) through the same macbook pro. Each of these teensies would be exclusively dedicated to reading a single capacitive proximity sensor and sending the output to the main teensy 4.1 (above).

I would like to achieve this by powering these teensies with a single thunderbolt port if possible, otherwise 2 is okay. None of the teensies would be overclocked, so teensy 4.1s would be run at 100mA each, and the teensy 3.2s would run at no higher than 50mA each.
 
plug a powered hub in and put all the Teensys on that? Maybe a Hub on the thunderbolt port would have enough power alone if it feeds on the higher voltage and presents it as 5V.

A powered 7 port USB 3 hub here has run at least 4 if not 6 T_4.0's and T_4.1's at times since they came out.

And TyCommander is awesome dealing with the multiples online to program or use as SerMon.

If a T_3.2 works - and the task is simple when using a T_4.0 it can be underclocked to use less power and will do more even at the same speed.
 
defragster said:
plug a powered hub in and put all the Teensys on that? Maybe a Hub on the thunderbolt port would have enough power alone if it feeds on the higher voltage and presents it as 5V.

A powered 7 port USB 3 hub here has run at least 4 if not 6 T_4.0's and T_4.1's at times since they came out.

And TyCommander is awesome dealing with the multiples online to program or use as SerMon.

If a T_3.2 works - and the task is simple when using a T_4.0 it can be underclocked to use less power and will do more even at the same speed.
Click to expand...


oh that is awesome to hear!!! so you or another poster has tried with at least a few teensy 4.1s on a hub ? Do you mind sending me a link to the hub you used or to the forum post you're referring to?
 
Without special power delivery negotiation, USB3 ports are supposed to be able to output 900mA at 5 volts. Older USB2 ports were generally designed for 500mA at 5 volts.

Of course, it's possible for modern USB3 ports to output far more power, but only if both devices communicate (with electronics inside the cable) to negotiate a higher voltage & current. But whether your Mac's port are even capable of negotiating to transmit such power is a good question. I do not know. But I do know the common usage is for your Mac to receive power that way. Most of the consume hub products you will find are designed with a heavy power supply and they transmit lots of power.

But even if special USB power delivery protocol isn't used at all, maybe you'll be able to find a hub which successfully receives up to 900mA and manages to properly power itself and transmit 100mA to 5 connected devices. The hard part is ordinary consumer products almost never have useful technical specs or reliable info about how they really work. You'll probably just have to experiment and run some tests where you watch the voltage delivered to each Teensy as you plug in more. Maybe also watch the hub's temperature. Even then, there's no real way to know if you're vastly exceeding its capability and just getting lucky.
 
Capacitive prox switches generally use 4 - 30 mA each. This is from 22 years of experience. The response time is generally well under 40,000 detects per second, under 400 is more common, so you can downclock your teensy to a minimum and you probably won't notice a thing. If you are using interrupt-based code instead of polling at a minimum clock speed, your power draw is likely to be extremely small. Think nA when idle waiting for an interrupts. A teensy is frankly extreme overkill for detecting a capacitive prox interrupt. If you are concerned about the distance, we are using them at over 100 cable feet at 24V for a normal proximity switch. The teensy runs into some issues if you try to use more than 1 mA passing through an I/O pin for good reason. You may be better off interfacing a teensy to an I/O serializer from TI or Microchip.
 
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