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Topic: Multiplexing SPI LINES (Read 1 time) previous topic - next topic

Lennyz1988

I am a bit confused can you draw a schematic or block diagram of what you propose.
I hope it makes sense. I never have created a schematic before. I noticed I forgot to connect the reset line, but that doesn't matter for this schematic.

The schematic is in the attachment.

Grumpy_Mike

Well I supposed I asked for it, it is not much clearer. For future reference make all wires horizontal or vertical and don't have wires going through components.

Now chips IC1 to 5 why are you only using one buffer in each chip. You have four identical buffers in each chip so that should simplify things. BUT you can not common the outputs of the buffers. I think you are getting mixed up by me saying common the MISO lines. You can only do this with the signal on the readers, this is because the chip enable line on the readers makes the signal on the readers tri-state when that chip is not being addressed. Once the signal goes through a buffer you loose that tri-state and they become normal signals that you can not join together because they are outputs. You will need separate receive buffers and you need to connect them to either different input pins or you need to multiplex them into one.

When drawing a schematic their is no need to show a chip with the pins in the physical order you can order them as you like as long as you number them.

Also with things like the buffers you can show each buffer individually, not all four joined together to make the flow simpler. The whole point of a schematic is to show the interconnections and signal flow. This does not mean a lot of rectangles with wires flying all over the place.


Lennyz1988

Well I supposed I asked for it, it is not much clearer. For future reference make all wires horizontal or vertical and don't have wires going through components.

Now chips IC1 to 5 why are you only using one buffer in each chip. You have four identical buffers in each chip so that should simplify things. BUT you can not common the outputs of the buffers. I think you are getting mixed up by me saying common the MISO lines. You can only do this with the signal on the readers, this is because the chip enable line on the readers makes the signal on the readers tri-state when that chip is not being addressed. Once the signal goes through a buffer you loose that tri-state and they become normal signals that you can not join together because they are outputs. You will need separate receive buffers and you need to connect them to either different input pins or you need to multiplex them into one.

When drawing a schematic their is no need to show a chip with the pins in the physical order you can order them as you like as long as you number them.

Also with things like the buffers you can show each buffer individually, not all four joined together to make the flow simpler. The whole point of a schematic is to show the interconnections and signal flow. This does not mean a lot of rectangles with wires flying all over the place.


Thanks you for your time and help. I really appreciate it. I ordered the line drivers and will try them out when I got the time. I don't have much experience in this and figuring this out will be harder than I originally thought. I will just make a prototype on a breadboard and test until I can get it to work.

In the mean while I will use 2 Arduino's connected through serial. That's something I can get working ;)

heyzazi

That is crap. All the lines can be common apart from the SDA, that is the one you must put through the multiplexer.

This is a circuit I used on a Raspberry Pi, it will also work for any 3V3 Arduino. If you have a 5V Arduino you must put a potential divider on each output pin from the Arduino to the reader. That is all the pins except Dout. And power the multiplexer with 5V.


i think this is answer for my project. i use 3 rfid too on my project, but i dont have much experience with this. so, i want to ask you about this. have u try it on arduino? and do you have sourcecode to multiplexing rfid with arduino? thank you, im sorry for my english..

Grumpy_Mike

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have u try it on arduino?
No but their is absolutely no way it will not work on a 3V3 Arduino.

If you have a 5V Arduino then you have to cut the 5V signals from the Arduino down to 3V3 with potential dividers before you feed them to this circuit. You have to do that anyway if you want to use these readers on a 5V Arduino.

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do you have sourcecode to multiplexing rfid with arduino
No but it is simply a matter of putting the binary address of the reader you want to talk to on pins 11, 10 & 9 of the 4051. So just three digital write instructions to select the reader.

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