I'm new to ARM, so I want to have a play with them by building a POV globe. It requires 380k_bytes of memory, so I have chosen the STM32H750 as my platform. When I first came across these boards on Ebay for £20, I searched for info about them, and I think I read somewhere that they can't be programmed through the USB, though I notice that they have a CH340C USB-Serial chip on them. If they can't be programmed that way, can program be transported to them on the SD card? I can't find any specifications for them on the web, but on the face of it, they look like a good solution to getting me started on this chip. I think I also read that they can only use one SPI channel, which would be a problem for me - but wherever I read these things, I can't find it again, and I'm not sure exactly what I did read.
Can anybody give an appraisal of these low-cost Chinese STM32H750 boards that are available on Ebay, Alibaba, etc?
mastack said:I'm new to ARM
Do you have experience with any other microcontroller(s) ?
mastack said:building a POV globe
Sounds rather advanced for a first project!
As with learning any new skill, it's always important to start with the basics and lay good, solid foundations. Then build up step-by-step.
Leaping in to something over advanced is likely to lead to frustration.
I would advise strongly against starting on cheap stuff from ebay!
mastack said:I can't find any specifications for them on the web
Of course you can't!
One of the key reasons they're cheap is that you get no support at all. You may not even get proper documentation. And it is unlikely that anyone will be familiar with it when you want help.
It would be far better to get a genuine manufacturer's development/evaluation/demo board - nowadays these are cheap, easy to obtain, some complete with a debugger and are documented and supported with examples, tutorials, etc.
ST have a vast amount of documentation & training resources on their website:
And from Keil:
You asked "Do you have experience with any other microcontroller(s) ?"
Not much. I worked all my life in computers, but on large systems. I worked in hardware, but always had an interest in software, and wrote a lot of C code (self-taught). Then, when I retired, I decided to have a go at microcontrollers, and chose the ATtiny85, and I specifically wanted to program it in Assembler. The first time you see a uC datasheet, it's quite daunting, and there's not a lot of Asm help about, so I struggled with it, but I successfully completed two projects - a Triac-based soft-start for my 240V table saw, and a mains timer using a relay. Its novelty aspect is that it can be set for any time up to 9 hours, and it is completely controlled and programmed with a single button. Once programmed for a delay time, it stores the time period into flash memory (program memory), so that period is used until it is programmed for something different. As my knowledge was hard-won, I decided to do a course on AVR assembler to ease the way for anybody else who wanted to tread that road, and the first video of the course describes the two projects, and is at
"Sounds rather advanced for a first project!"
Well, it will be my third. I would do it with an AVR controller, but there are none with enough memory - or fast enough. I will require 372k_bytes, and I need to drive two LED strips at 22 MHz each. I chose the STM32H750 because it has memory, and two SPI's to drive the LED strips. (Each LED in the strip takes 32 bits of colour data, 105 LEDs in each strip).
"Leaping in to something over advanced is likely to lead to frustration."
I'm fully expecting a lot of that, but time is on my side - no deadlines! One way or another, I think I'll get through it - though there will be pitfalls along the way, and, I'm sure, I will need help a few times on this forum. Nonetheless, though the chip has huge potential, I won't be using much of it. The POV globe is made by rotating a semi-circle of LEDs, so there will be a timer to measure the rotation period, a PWM output to drive the motor, and the two SPIs for the LED strips. It will also need an SD card for more images - but that was an attraction of the Chinese board.
"You may not even get proper documentation." It's possible that they just arrive as a board with no docs at all. That's why I was asking before I shell out to get one. They're only £20, but I don't want to waste it. On the other hand, though I hear what you say about spending a bit more and getting something that will work and can be used, I'm sure you'll understand if I tell you that I'm retired and living on state pension, so I don't want to spend more than strictly necessary on something that I don't expect to ever bring me any profit - or a salary.
Thanks for the links. Now that you know my intentions and circumstances, what platform would you recommend? The only one I have seen with a 32H750 is the Chinese one. I may have to design a board and get it made, and that will involve learning how to interface an SD card as well.
If you would indulge me, could I ask a couple of very basic questions here?
1. I will be driving the SPIs in master mode only - data out, nothing will be coming back. I have calculated that I need 22 MHz, but if I take it much above that, I think I'll start losing data along the LED strip. How do I set the frequency? Will I need an external clock?
I'm not asking for a detailed answer - a one-liner will do fine.
2. The memory will contain the video image of one complete rotation of the semi-circle of LEDs. Can I use DMA to get memory to the SPI interface? I see in the datasheet that DMA is limited to an address range of 64k, so I guess the program would have to reload it 4 times. I hope there's a "DMA-complete" interrupt!
mastack said:time is on my side
All the more reason to spend time on laying good foundations to start.
mastack said:I will need help a few times on this forum
Think carefully about which forum is appropriate.
Most of this has nothing to do with ARM - you would be better off on the ST forum.
mastack said:They're only £20, but I don't want to waste it
ST's own discovery boards are on that order - and do come with full documentation, support, built-in debugger, etc
Some include SD Card.
mastack said:could I ask a couple of very basic questions here?
could I ask a couple of very basic questions here?
Those questions would be far better asked on the ST forum: they are specific to the ST part - nothing to do with ARM.
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