Minimal circuit for i.MX RT1064 using USB power

[AUMO]

I would like to build a small low latency device that captures video with a high speed image sensor (480fps), detects simple objects, and passes on the coordinates via USB (HID) to another device. If I understand correctly, the i.MX RT1064 MCU provides most of the functionality necessary to build such a device, it even has Flash memory to hold the program code.

I understand that the recommended way of designing a custom device is to start from the circuit of the Evaluation Kit (i.MX RT1064 EVK) and to gradually remove all the parts that are not needed. Unfortunately the evaluation kit has so many components that I find it hard to strip it down. Therefore I wanted to ask if there would be a way to obtain the opposite of that, a minimal circuit for i.MX RT1064 that would only contain the components needed for programing and solid power delivery by one single USB port.

[EdSutter]

Have you considered the Teensy4.1? 

It is reasonably minimal, and I believe its pinout will support a camera interface.

It is a '1062, but has an external 8M flash.

If that circuit works, then you just build a carrier for the Teensy.

Ed

[AUMO]

Thank you @EdSutter so much for this suggestion. I found the teensy 4.0 schematic on their website (smaller than the teensy 4.1) but unfortunately this design also overwhelms me. it has about 50 parts. I was hoping to get away with something like 10 parts (crystal plus a few resistors and capacitors) in order to make the device smaller. Is it really necessary to have so many parts to get the i.MX RT1064 stably operational as a USB gadget?

[EdSutter]

I have not personally done any HW design with the IMXRT1060 family, but I doubt you will get much smaller a design than the teensy4.0.  Aside from discrete R/C/L components there are two additional parts: SPI-Flash and a small microcontroller (that I believe would be purchased from pjrc.com) that essentially guarantees you won't brick your design.  That that 2nd microcontroller connects to the 1060's JTAG and can be used to pump in a new image regardless of the state of the 1060.  You can probably get more info from pjrc.com.

Anyway, I'm not a HW guy (nor do I even know the folks at PJRC, I just like the design), but my guess is the abundance of R/C/L is just the fact that its a 600MHz device, so you're not building a typical arduino-like device.

[AUMO]

I did not know about the requirement for an additional micro controller. Given that in the documentation of the 1060 it is written that it supports USB, I thought it had all the necessary hardware on board to actually serve that interface (e.g. as a USB gadget). Apparently this is not the case. Thank you so much for pointing this out.

[EdSutter]

Sorry if I confused you...  No,  the 106x doesn't "require" that microcontroller, its just part of the teensy design to support easy firmware downloading.

[carstengroen]

@AUMO ,

did you (at all?) look at the schematic/board I posted below ?

The RT106x are fully capable if acting as a USB device (and Host for that matter). Look at my schmatic, this is from a working board (and very simple)

[AUMO]

Yes, I looked at it and while I understand that for you it is simple, for me it is very overwhelming. It has so many chips (U2A, U3B, U3C, U3E, U3F, U3D, U1) and dozens of RLC. I was (apparently unrealistically) hoping for a schematic with the 1064, a USB plug and a few components (hopefully < 10) connecting the two (for a total size of the pcb of about 2cm^2).

[carstengroen]

@AUMO 

Well, U2 is the voltage regulator (you need that one as USB is 5V and you want to supply your CPU from that voltage). U3 is the CPU, which you obviously need (You do realize that U3A, U3B etc is one single chip, right?). U1 you can omit, its a HyperRAM that you don't need in your case. So you are down to 2 chips! XTAL1 you can also omit (32 KHz xtal for the RTC). L1 is needed for the internal switchmode powersupply of the CPU. The resistors and capacitors are more or less all needed (you can remove those around U1 if you omit U1). If you are still overwhelmed, I strongly suggest to start with a simpler CPU (LPC54606 needs no external components to run, except the volatge regulator for the 5V USB).

[AUMO]

Thank you so much, this answer clears up quite some things. It also proves that I am not in the position to understand these kind of circuits without someone leading me through the design step by step. Just to give an example, I assume that the reason that you use capacitors in parallel (C30:C28:C29, C11:C12, C23:C26, C13:C14) is that there is no single capacitor with the desired capacitance, but I am not even sure of that Thank you for suggesting the simpler CPU LPC54606, I didn't even know that some of those chips are easier (with fewer parts) to incorporate into a circuit than others.

[carstengroen · Accepted solution]

@AUMO 

Not to discourage you, but you are not going to get a design going with the RT series (in BGA) if you are at that level currently. This is not meant anyway negative, but there a ton of stuff you need to master before going that route. The capacitors in parallel is NOT because you can't get a single one at the right size, the number of capacitors are spread out on the design to bypass the individual pins on the processor etc.

Even if you get this, there is still a immense job of doing a design and layout of the chip, and after that, soldering it. I would strongly suggest starting with something simpler, f.ex the LPC54606, or maybe even better, a LPC1549 (which is smaller, 48 pin and also has a USB interface). There are many many more processors with this, these are just some that is on top of my head (that I use on a daily basis)

The testboard I did for the RT device is seen from the back, there you can see even more bypass caps located close to the pins they need to decouple of the CPU:

[victorjimenez]

Hello AUMO, 

Unfortunately, we don't have any other design schematics besides the ones from the RT1064-EVK. So, the way you start is a good way to do it. Start from those schematics and begin removing all the peripherals that you don't need on your board. But keep in mind that you don't want to remove things that the RT needs to work properly. For this purpose, the Hardware Development Guide would be the document to look at. 

Link to the Hardware Development Guide. 

Regards, 

Victor 

[AUMO]

Thank you so much for your fast answer. The link helps me a lot but it also leaves a lot of open questions. There are two circuits depicted, one containing the 2SK3018 and one showing the actual USB plug, but the latter is denoted for USB Host mode only. I am only interested in using the MCU in device mode, sorry for not mentioning this in my first post.

I know that a lot of thought goes into power circuit design and for me those aspects are hard to understand given that I am a computer scientist. What I am looking for is one single circuit diagram that contains the i.MX RT10XX MCU (working only in USB device mode), the USB plug and all the components necessary to connect the two (ensuring solid power delivery for consumer mass production). If anyone in this forum has such a schematic, I would be very grateful.

[carstengroen]

Aumo,

I don't know if you can use some of this, but this is a first "minimalistic" board I did for the RT1064 some time ago. It works. There are no camera interface etc, but it shows the minimum required for USB device at least. Please note that this is NOT perfect in any way, it was only meant to be a quick and dirty testboard to check the RT1064 (and HyperRAM) out

Schematic attached

Use at your own risk...

[vasudhevan]

Hi @AUMO,

       Instant of imx rt evk circuit you can refer attached link https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/USB-Power-Control-of-i-MX6ULL-EVK/ta-p/1....

       If you are implementing single usb otg host/device you can choose mic2025 series http://ww1.microchip.com/downloads/en/DeviceDoc/mic2025.pdf

Regards,

  Vasu