BP carrier card advice needed

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visinet
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BP carrier card advice needed

Post by visinet » Thu Dec 14, 2017 5:19 pm

Hi all;
I need to replace my current HW system for a product that I manufacture and am looking into doing that by getting a carrier card/breakout board designed for the Blue Pill (BP) and am asking those of you that have experience with this type of project for advice/feedback on what type of effort this will really require so I can assess if I really want to move forward. Here are the general board specs:

1) Be all through hole unless absolutely need to use some SMD
2) Will have 16 Relays on it to be able to send System 24V control signals out to external world for equipment control. These are pulsed on/off for about a second to control external relay and are run to a 37pin DSub connector on the board that protrude through the rear of the products chassis.
3) Will have 16 opto-isolated inputs to monitor external contact closure equipment status points and are run to another 37pin DSub connector on the board that protrude through the rear of the products chassis.
4) The Relays and Opto IO will be accessed through 2 MCP23s17 IO expanders via SPI 1 of the BP @ say 2Mhz
5) ALSO, send this SPI 1 bus to connector so that multiple of these boards can be used in a single system to increase the IO count.
6) Send the BP’s SPI 2 ports to header connector to connect/interface to spi based Front Panel
7) Have 3 10pin headers and driver chips to provide 3 jumper selectable UART RS232/422/485 serial ports from the BP
8) Will take in 2 24Vdc switcher supplies, diode-or them together to produce a redundant system wide 24V.
9) Tap off each 24V input, adjust down to 3V, buffer it, and finally send to BP ADC so sw can monitor system input supply voltage levels.
10) Rectify the system 24V down to 5V and 3.3V for system required voltages
11) Provide connector to send all 3 voltages to other boards when used in a multi-board configuration. Only 1 board, the master with the BP connected, will have the active power system and will provide all the power any additional boards

That is basically it in a nutshell. %90 of the circuits already exist in the current solution so there is not much design needed other than the current system is memory mapped IO and the new one will be serial SPI based. I am a SW/FW guy and not a PCB designer but have done some basic PCB stuff in the past. These requirements and the related circuits appear pretty straight forward to me, not like some complicated high speed RF….. type of system so I would think that the PCB design and layout would be pretty straight forward and not require all that much expertise. This will be used in my commercial product so it is not a hobby activity and needs to be rock solid and reliable.

So, here are my questions. Any and all advice will be greatly appreciated.
- Am I under estimating the complexity of this job?
- Could this be done with only 2 layer board or is that unreasonable and will require 4 layer
- What type of effort , time and cost, would you expect to be to get to the point I am ready to order 1st boards to test
- Do you see any problem areas that need to be looked at closely?
- Anyone have this direct type of experience that would like to investigate taking this project on? If so please send me a message and we can start a dialog.

Thanks so much for all your time.

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RogerClark
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Re: BP carrier card advice needed

Post by RogerClark » Thu Dec 14, 2017 8:19 pm

It just sounds like a very big, rather than a very complex board.

I see no need for 4 layers. It’s amazing what can be done with just 2 layers and the cost of 2 layers is around 5 to 10 times less than 4 layers.

The only thing that sounds potentially problematic is the supply noise, e.g. loads of relays making spikes, as well as multiple rails.

You are also using most of the Blue Pill’s pins, so I would check if you actually have enough pins, or whether you need to use a F103V board, like Victor has for his 3D printer controller

visinet
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Joined: Mon Dec 05, 2016 6:30 pm

Re: BP carrier card advice needed

Post by visinet » Thu Dec 14, 2017 9:17 pm

Roger;

Yea, I figure the board will be somewhere around 6x6 or 6x8 in size and I will be using most every single pin on the BP. I have never had any noise issues with the relays up to now so I didn't think that could be an issue. The relays will be driven by ULN2803 which have internal protection flyback/snubber diode, so that should not be an issue, and the external devices they drive also employ flyback/snubber diodes to protect my drive signals. What kind of problem did you think I could run into?

My biggest concern is the serial/SPI interface to all the IO(relays and optos). My current system is HC11 based with everything 5V and memory mapped and I am worried that I could run into problems due to using serial SPI bus. I know that it shouldn't be an issue for a single board solution, but I'm not so sure about about running the SPI buss to other boards in a multi-board configuration, even when we are only talking about adding a few inches to the buss length. I am pretty sure that if the system is designed and laid out properly then the SPI stuff should be rock solid, however this is one of the key areas I wanted advice from the community on. For someone that is experienced and has done this before, I would think they could provide a quick and accurate assessment of this area.

Thanks for your response.

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RogerClark
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Re: BP carrier card advice needed

Post by RogerClark » Thu Dec 14, 2017 10:04 pm

I'm not sure why you are using SPI. Is it to give you more channels ? Using a board with more GPIO's would be easier.

I think the questions about bus length etc, are general PCB design and you are more likely to get advice on a forum like EEVBlog which has dedicated sections.

This forum is primarily about Arduino running on the STM32, but about hardware design.

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mrburnette
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Re: BP carrier card advice needed

Post by mrburnette » Fri Dec 15, 2017 1:24 am

visinet wrote:
Thu Dec 14, 2017 5:19 pm
Hi all;
I need to replace my current HW system for a product that I manufacture <...>
The Chinese "blue pill" may be an unwise choice if your product needs to be manufactured over more than 1 production cycle. I strongly recommend sourcing the uC directly, STM32F1xx. There is little on the blue board that cannot be replicated directly on your larger systemboard. The bluepill could vanish from the marketplace at anytime.
You can very easily manage the uC installation using only a hot air rework station, under $100 U.S.D. Of course, you "can" use a fine-point iron, but the final results is never as good as hot air.

You did not specify the original uC, but if it were 5V, then you must take into affect that the STMF1xx is 3.3V ... noise that was never an issue in the old design may be a problem in the lower voltage environment.

Discount if not applicable: I do not see an analog requirement, but generally speaking the analog reference should not be the board 3.3 Vcc ... rather a separate reference source is desirable.


Ray

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