D-Sub signal access

Question

I want to be able to interrogate the signal on each pin of any D-Sub cable, therefore I need to know what hardware do I need to get from the D-Sub input to the Pi?

I have yet to purchase my Pi, but at this time plan to get a 3B

I also hope to be able to connect it to my PC Monitor and install windows 10 with Visual Studio on it.

Thanks for any suggestions you may have.

genebren · Answer

Daniel, Both dougw and beacon_dave have excellent suggestions. I can understand that using the Raspberry Pi offers some interesting benefits, in that you can build a standalone tester/documenter for your cables. Using the first suggestion, the decoders are used to extend the GPIO, such that 5 GPIO will yield you 32 addressable outputs. Depending on how many outputs you add in this manner, you may or may not need to also add the expanders for additional inputs. There are other similar devices that could be used that are I2C expanders, again giving you addition GPIO-like pins, addressed by I2C commands. The second suggestion could also be used with the Raspberry Pi, where the MEGA 2560 device could be used as a co-processor to the RPi. The RPi could communicate with the MEGA2560, and tell it which pins to drive and which to sample. Or given a more complex program, the MEAG2560 could be command to scan, and the return the pin-to-pin readings back to the RPi. There are quite a few options, which may or may not work for you depending on your understanding of electronics/programming. Good luck sorting out these options. Gene

beacon_dave · Answer

A R-Pi sounds a bit overkill for this task.

An Arduino Mega 2560 will give you 54 Digital IO pins and may be of interest if you don't want to have to expand the number of ports:

https://store.arduino.cc/arduino-mega-2560-rev3

Shift registers might be another way to go:

https://www.electronics-tutorials.ws/sequential/seq_5.html

and you can always use the likes of the I2C bus to expand the number of ports available.

dougw · Answer

You could use dual 16 bit decoders to get 32 output bits from 5 data bits.

You will also need a 32 bit input expander.

https://learn.adafruit.com/mcp230xx-gpio-expander-on-the-raspberry-pi/using-the-library

Robert Peter Oakes · Answer

2 of these and the price of 4 mcp23s17 https://www.tindie.com/products/RobG/32-io-expander-booster-pack-pcb-mcp23s17/ Add you controller and the D Type connectors Bit of programming and your pretty much done except for an enclosure

planedan · Answer

Thank you. I think I have what I need to wire the D-Subs to a breadboard, and have looked into the GPIO, but still do not see that it is possible to pragmatically energize each of the pins and subsequently record the result, ie when pin 1 is energized, pin 7 on the other end sees it. Thinking that if I had 50 GPIO pins and a 25 pin D-Sub cable, then GPIO 1 would be input ( energizing voltage) for d-sub pin 1 and GPIO 26 would be output from from d-sub pin 1 on the other end. Thus, when my program sends the voltage to GPIO 1, whatever GPIO that was connected to the d-sub pin that sees the voltage, would respond high when the loop of the program asked for the state of that particular GPIO. However, we only have 40 GPIO and it appears that many of them are already spoken for.

So, is the Pi capable of doing what I want to do?

Thank you for your time.

rew · Answer

I have an STM32 development board. A client has asked me to support a "game" where users will plug connection X to connection Y using banana plugs and the software will do some bells-and-whistles things when the solution is found.... You basically need 50 IOs to achieve your application: up to 25 on connector A and up to 25 on connector B. I have an upgraded board that has 64 IOS.... and an USB port to connect to a pi or PC. You would be responsible to build the D-SUB connector blocks. D9-1 - D15-1 - D25-1 - STM-1 So, pin1 of the 9-pin connector goes to pin 1 of the 15 pin connector and the 25-pin connector. And to the board. Similarly you connect all pin2's and so on.... (after pin 9, the dsub-9 no longer plays along...)

planedan · Answer

That seems good for what I want to do. How does the STM32 play in this and what is a STM-1. I already have the D9, D15, and D25 connector blocks and plan to mount them on a board of some kind, this weekend. I planned to put an euro connector strip between the A D-Subs and the board that goes to the Pi. Pin A-9-1 goes to euro connector slot 1, along with A-15-1 and A-25-1 and so on, which is sort of what you were describing. You only test one cable at a time, 1, 15, or 25 So, is this upgraded board, for sale? Thank you.

Robert Peter Oakes · Answer

Then you dont need 50 active IO pins from a micro controller. You need to be able to activate one of 25 pins from one end of the cable and scan the other end (25 Pins) for the active one or many or none, depending on how it is wired. this means you need something like this use MCP23S17 SPI serial to 16 port IO expanders, this are cheap and well know for programming with any micro-controller with a SPI interface, this includes almost all Arduino's, Raspberry PIs, Beagle Bones, ESP8266 etc etc. build the chips onto their own board and you have a scanner usable with whatever processor you like even without a SPI port, the control signals could be BIT Banged out. each MCP23S17 with its own SPI address (Built in functionality), 2 used to control 32 outputs and 2 used to read upto 32 inputs as these chips are programmable you can come up with creative ways to scan the cable including looking for diodes in circuit etc, What you dont need to find is a single SBC with 50 or more IO pins available, thats just a complete waste of money and overkill, this way allows any micro-controller from cheap small to large expensive. the code to scan the pins would be very easy to do and take very little space

rew · Answer

Most modern embedded controllers (so everything except the CPU that goes into your PC) has a whole bunch of pins that can be programmed input/output high, or low as you please. General Purpose Input/Output. Most of these can have a few other functions. So on the pi P1 port there are pins that can do SPI or I2C as well as their general purpose IO. But if you don't need the I2C, they can be freely programmed to do whatever you want.

genebren · Answer

You might be able to use something like this: https://www.ebay.com/i/111873783565?chn=ps If you can further explain your need, I might be able to help you further. Good Luck, Gene

rew · Answer

I have adapted the firmware on my STM breakout board for 64 IOs and checking connectivity. Note that it will check everything. So for example you'll learn when a cable connects DTR to RTS in the connector on one side. If you declare 26 pins (i.e. one dummy) on one side, and 26 on the other side, the identifications for the connectors will be a-y on the first connector and A-Y on the second. A nine-pin simple DB9 cross over (null modem) cable will then show up as Bc Cb Ee Connecting DSR with DTR on each end (i.e. locally inside the connector) then adds "DF df" to the reported connections. The STM board provides a virtual com port that reports "puzzle 5: Bc Cb Ee DF df" when suddenly that null modem is inserted. The "5" means that it counted 5 changes against the previously reported state. You can send "fb
" to the board to force a reporting cycle.

genebren · Answer

Here are some clever little breakout boards that you can populate with D-sub connectors (male or female). You could use these with a raspberry PI prototype board to interconnect the pins to the raspberry pi.

Proto PCB for 9-25 pin D-SUB Connectors

You could also build a fairly simple PCB to do all the interconnections for you.

Good luck,

Gene

mp2100 · Answer

You can certainly connect your Pi3B to your PC monitor, with HDMI (or an adapter if you don't have HDMI). But the Pi only supports Win10_IoT Core:

https://developer.microsoft.com/en-us/windows/iot/downloads

Of course, maybe you can do Windows 10, there's this:

Windows 10 on ARM on a Raspberry Pi 3B 'Proof of Concept' with Full Windows Desktop