AD75019 16x16 crosspoint switch/multiplexer cannot communicate via SPI
Posted: Mon Feb 12, 2018 8:13 am
HI guys!
I am trying desperately to get the AD75019 analog crosspoint switch to respond to bit vectors sent via SPI from a Pyboard but for the life of me I can not get it to do anything it should.
The datasheet is here: http://www.analog.com/media/en/technica ... D75019.pdf
My wiring is:
AD75019 pin : Function
1 : pboard pin X5 SS
2 : pboard pin X6 SPI CLK
3 : pboard pin X8 SPI MOSI
4 : -12v + 100nf cap to gnd
41 : +12v + 100nf cap to gnd
42 : +5v + 100nf cap to gnd
43 : GND
44 : not connected
My code simply sends a vector of 32 bytes, i.e. 256 bits, with all bits set to zero. This should turn off all the switches, but I measure the resistance across input X0,Y0, i.e. AD75019 pins 15,31. The results are strange: sometimes I get 5Mohm, sometimes 30ohm...
If I send a vector of 255, i.e. all bits set, then I usually get 55ohm across any pair of inputs.
If I send a vector of 31 zeros, and a single" one", it should connect X0,Y0, but this result nearly never occurs, sometimes, it may work once, but then on the next send, of 0s, then a single 1, fail.
I have tried various SPI clock prescaler values from 32 to 256 as per the data sheet. I have tired all combinations of polarity and phase, and the results seem to be random, but never as expected.
I feel that I must be missing something very simple, but for the life of me I don't see it
Would anyone have any thoughts?
Cheers,
Bob
I am trying desperately to get the AD75019 analog crosspoint switch to respond to bit vectors sent via SPI from a Pyboard but for the life of me I can not get it to do anything it should.
The datasheet is here: http://www.analog.com/media/en/technica ... D75019.pdf
My wiring is:
AD75019 pin : Function
1 : pboard pin X5 SS
2 : pboard pin X6 SPI CLK
3 : pboard pin X8 SPI MOSI
4 : -12v + 100nf cap to gnd
41 : +12v + 100nf cap to gnd
42 : +5v + 100nf cap to gnd
43 : GND
44 : not connected
My code simply sends a vector of 32 bytes, i.e. 256 bits, with all bits set to zero. This should turn off all the switches, but I measure the resistance across input X0,Y0, i.e. AD75019 pins 15,31. The results are strange: sometimes I get 5Mohm, sometimes 30ohm...
If I send a vector of 255, i.e. all bits set, then I usually get 55ohm across any pair of inputs.
If I send a vector of 31 zeros, and a single" one", it should connect X0,Y0, but this result nearly never occurs, sometimes, it may work once, but then on the next send, of 0s, then a single 1, fail.
I have tried various SPI clock prescaler values from 32 to 256 as per the data sheet. I have tired all combinations of polarity and phase, and the results seem to be random, but never as expected.
I feel that I must be missing something very simple, but for the life of me I don't see it
Would anyone have any thoughts?
Cheers,
Bob