16x16 Analog Crosspoint Switch using two MT8816's

I bought some of these 8 by 16 analog switch arrays so I can say take an input signal and send it to a certain output or a different output or multiples at once and just have all kinds of options but I want to be able to have 16 by 16. so I did a representation here if I take two of these 8 by 16 array chips and I connect all of these 16 x's in parallel and then I keep all of the Y's independent I've essentially created one large 16 by 16 Matrix and I can individually address one chip or the other chip based on which y path I want to control so in order to make this easy to work with especially because I'm using two of these chips I made a PCB with today's sponsor PCB way so I have 16 x and 6 16 y pins along with a corresponding ground that I can use to bring a signal in or take a signal out with a ground reference and to control these chips I'm using an mcp23017 gpio expander over I squared C so I'm using an off-board Arduino Nano in this case just to control this Matrix and I have it set up to Take 5 volts in and there's an onboard negative 5 volt generator with the icl7660 chip so that way I can send in an AC audio or even a video signal or something that needs to go above and below ground as long as I keep it in this case within plus or minus 5 volt swing I can pass that through this Matrix freely so some example uses of this if I have a test setup where let's say I have an audio amplifier connected to y14 so it's waiting for an audio signal to come to Wi-Fi 14 and it goes to an amplifier I can have say a bunch of different test sine wave signals set up at different frequencies and I can control this Matrix so that one by one these different sine waves are sent to the audio amplifier so I can hear that everything's working as expected or I can have an oscilloscope on some other pins and I can look at those signals and at the same time send it to an amplifier and see as well as here the signal Integrity we won't dig too much into all the specs like what kind of voltages can this chip run at but one thing to note because this is an electronic switch it's not like a bunch of relay contacts or other mechanical switch contacts with minimal resistance we need to consider that when we close a circuit path we're inserting some resistance and we need to look deeper in the data sheet if I'm running at 5 volts when vdd is 5 volts the on state resistance of a switch at room temperature could be between 120 average or up to 185 ohms inserted in line with your signal so that may be okay if you're taking either audio or video signals sending them through here but you've got buffer chips helping regenerate a new ideal lower impedance output signal anyway it may not matter if you've got one or two hundred ohms in line for Signal Integrity reasons but if you're doing something that may care about the impedance such as if you're using this to switch a bunch of guitar effects in and out of a guitar path to an amplifier every time you add another effector you might be adding another one or two hundred ohms in line with your guitar signal and there's also capacitance involved so routing a guitar signal through a bunch of effects using something like this it could be the same as adding several feet of guitar cable which may or may not matter but it could come into play so something to be aware of so depending on the application in mind you can look through a data sheet and see if this chip will do what you need but otherwise we need a bunch of control signals from our gpio expander so whichever chip we're talking to we use a chip select and we set the data for either opening or closing the switch contacts at a certain point on this grid and whatever specific switch on this grid we are talking to that is set by these X and Y address pins so if I want to open or close the contacts right here on my overall larger grid I need to use chip select to only enable this chip then I need to use those address pins to say I want this x position and this y position on the grid and I want to either with data open or close that contact here's the schematic we got our I squared C clock and data going to this gpio expander block we got 5 volts coming in and we're using the 7660 to generate negative 5 volts for those Matrix chips so that along with plus five we have negative five and we can have an analog signal swinging above and below ground the gpio expander will take the commands over I squared C and control the X and Y coordinates of something we're trying to do use chip select to go to the correct chip so that we can handle a larger grid of 16 by 16 and we set the data and strobe it in to control the switch and if we want we can just reset everything and open all switches the gpio expander is the exact same circuit block we use all the time when we're using this chip I squared C pull ups address pins which I just keep at the default all jumpers installed so zero zero zero and I tell the sketch what address this is and we just have our outputs coming into the other circuit block to control these Matrix chips and the X's are all in parallel between the two chips so if I have a signal going to X1 it's going to appear at X1 on both chips but when deciding which y to route that to let's say I want it on this overall grid the X1 pin I want it to go to actually y7 so I need to turn on this contact here this chip on the left is y 0 to y7 the way I wired it up the second chip is Y8 to y15 on my overall bigger grid so to go from X1 to y7 I need to close the contact right there so I would set the address pins here to be X1 and y7 but I'm going to enable this chip and not enable this chip so this one actually closes the switch between X1 and y7 this one does nothing so we end up getting a connection right here but if I want to control X1 going to y15 that's really y7 again but on the second chip so I would just not enable this one I would enable this one and I'm still saying X1 to y7 on the addresses but now the X1 here is ignored here and it does get connected to y7 over on this enabled chip so that's how we combine the two chips to make one larger 16 by 16 grid now looking at a test example I set up I have a function generator we're just sending in three different signals on the X pins and I'm taking four outputs along the Y because I have a four Channel scope and in the demo sketch I'm just switching various nodes here to connect either the sign or the ramp signal out to various scope channels in the demo I have a function I call for set The Junction and I give it an x and y coordinate and decide if I want the junction closed or opened so if I call set Junction 0 5 and closed that means x 0 and Y 5 right here is going to be connected so I'm taking this sine wave and sending it to that scope probe whichever one it happens to be connected to then the next thing I'm doing in the demo is closing the contacts between x0 and Y8 so that is right here so now I've already got the sine wave going out to one scope probe now I'm just enabling the same sine wave to connect to a second scope probe to demonstrate that you can send one signal to two outputs and for this scope probe here I'm switching back and forth between a sine wave and a ramp wave so I'm just basically exercising the ability to turn channels on and off I took a test sine wave on one of the channels and I overlapped the function generators sine wave on top of one of the Y outputs and I didn't see really any Distortion or Jitter of any kind or any change in amplitude between input and output of the Matrix all the way up to one megahertz at least that's as far as I went for the second demo but this time I'm actually using it for a guitar signal although ideally I may want relay contacts in a matrix for guitar audio but for a proof of concept this is the grid with no contacts enabled so I have this configured so all of the X are input signals all of the Y are outputs so each of these guitar effect pedals Distortion delay and a flanger can take audio coming out of the Y pin and the audio will go into the effect then it can come out of the effect and go in on a certain X so I can change the signal path I can do what I want and the first thing I do is close the contacts at x13y13 and wait five seconds so when I close the contacts at X and Y 1313 I'm sending the guitar signal straight to the amplifier with no effects [Music] and now I want to add the Distortion effect in line between the guitar and the amp so I need to release this node here so I open the contacts at XY 1313 now I close the contacts at 13 and 2 so x13 and Y2 will create a path from the guitar to the input of the Distortion effect I'm also closing X and Y 2 and 13. so the output of the Distortion goes to X2 and I've now closed a path on y13 So guitar to Distortion and Distortion to the amplifier so basically then one by one I can then add a delay effect after the Distortion and go out to the amplifier or then I can also add a flanger after the delay and have the flanger finally go to the amplifier so at that point what we have is a guitar going into a distortion then a delay then a flanger then to the amplifier through this Matrix normally what you would do is just stomp on the pedal that you want to turn on or off but if you're doing something where you need to switch all three of these on or off at the same time you'll end up tap dancing and other inconvenient things can happen or maybe what you want is to switch this between this amplifier or a different amplifier connected on another y Channel or another use case would be if you actually want to change the sequence of these effects so instead of guitar straight into Distortion and then to the delay maybe for certain cases you want to swap those so you're going guitar into delay then into Distortion and then over to flanger because it can sound differently depending what you're doing so in that case you would have to go and unplug and replug different cables so that's where the flexibility of something like this comes into play so here's how this sounds starting from a clean guitar all the way to all the effects on [Music] [Music] so that's a couple of possible uses for an analog switch like this I figured having 16 inputs and outputs would give me more than enough to experiment with and it seems like this worked out well

Channel: Gadget Reboot

Views: 1,934

Keywords: mt8816, crosspoint switch, analog switch matrix

Id: FYjVVteUiZY

Length: 13min 8sec (788 seconds)

Published: Fri Sep 01 2023