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Author Topic: replace SD card with USB stick  (Read 1708 times)
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Ooh - two of these per master would be good.

What do you mean by 'master'? PC and 'Sparkfun'?
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VUB300 and sparkfun, the guys that actually interface with the card.
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VUB300 and sparkfun, the guys that actually interface with the card.

Excellent. Well understood!

So, I'd need two ISL8499 chips for each master, and then connect
VUB300_D0, VUB300_D1, VUB300_D2, VUB300_D3 to ISL8499#1
VUB300_CMD, VUB300_CLK to ISL8499#2
spark_D0, spark_D1, spark_D2, spark_D3 to ISL8499#3
spark_CMD, spark_CLK to ISL8499#4.

On which pins would I have to connect them on the ISL8499's? I suppose either the NO or NC contacts?
Which pins would have to go the SD socket?
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A little messy, but you get the idea?


* SD_muxing.jpg (45.45 KB, 960x720 - viewed 20 times.)
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Got it!
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Ooh - two of these per master would be good.

Confused me a bit, I understood I'd need 2x2 chips, but got it now'.

How would you switch between the 2 masters in this configuration?  As I don't see enable contacts on the chip as suggested with the previous suggestion? smiley
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Never mind, I overlooked the IN1-2 and IN-3-4 contacts. Awesome. Thank you so much!

What about the write protect and command pins? Everything in parallel?
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Would this chip be an alternative for the ISL8499?

http://be.farnell.com/texas-instruments/ts3a5018dbqr/switch-analog-quad-spdt-ssop16/dp/1236585

I generally look for my components at Farnell, don't have experience with digikey. I'm suspecting I'd have to pay customs to have it delivered to Belgium, so if I could find a good alternative at Farnell, that'd be easier smiley

EDIT: or this one? http://be.farnell.com/analog-devices/adg711brz-reel7/low-voltage-quad-spst-i-c/dp/2376782
That one supports a greater range of voltages (1.8V to 5.5V).

What would be the specifications to look for?

EDIT: I drew something up in Eagle. Does that seem correct? www.jensvanhoof.be/SDinterface.pdf
« Last Edit: March 13, 2014, 08:35:57 am by jensvanhoof » Logged

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Earlier question - yes, the selection lines weren't shown. How you select is up to you - physical switch easiest as neither side has a control line you can program.
WP & CD - gonna have 8 IO, can switch those too. Or connect to both devices,  the pins are typically just connected to Gnd via switch when the card is put in the socket.

The TI part is kind of high resistance - but the current being switched is low so you shouldn't get much voltage loss across the switch.
The Analog Devices, you need 3 (6 signals) or 4 (8 signals). The TI, you'd only need 2 total (8 signals).

Spec to look for is Low resistance, single power supply.

Not sure what part you used for the switch, but you have idea.

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Hi again,

I purchased two of these chips:
http://be.farnell.com/texas-instruments/ts3a5018pwg4/switch-analog-spdt-quad-10r-smd/dp/1494943

I soldered them onto 2 breakout boards and tested the functionality. It works as expected if tested without any connection to the pins. You can see them integrated in the prototype (left and right from the 3.3V regulator):


The 6 contacts that I need to switch (4 over chip#1, 2 over chip#2), are brought to the 12 headers just to the right of the SubD9 connector. If I switch the power on like this, it works. Using a multimeter the upper row contacts connect to the bottom row, connecting all 6 lines.

I modified then the Sparkfun's board, cutting the 6 lines that run from its processor to the SD card, and bringing them to the headers on the board (T1-T6). I cut the original lines to those contacts, as I don't need them in their original function. In this picture you can see the modification (I put jumpers on the headers to test the board):



This works as well, as if there was no modification performed.

However, when I connect the 2 things, it doesn't work. The processor cannot read the SD card anymore. When I use my multimeter to 'bleep' the resistance between the two rows, it measures no connection. Like the switch(es) not performing their function anymore.

I don't really know what's going on. Any suggestions? None of the 6 voltages exceed V+ of the switch (3.3V).




* DSC00991.JPG (154.31 KB, 612x459 - viewed 21 times.)

* DSC00993.JPG (172.99 KB, 612x459 - viewed 39 times.)
« Last Edit: March 18, 2014, 03:03:48 pm by jensvanhoof » Logged

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Many of us cannot see the pics. Can you Modify your post, click Additional Options, Browse to your locally stored pics and Attach them?
Describe how you are controlling which switch is selected.
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Many of us cannot see the pics. Can you Modify your post, click Additional Options, Browse to your locally stored pics and Attach them?

Done!
I've put the control lines of the 2 chips together and pull them up to V+ using a 10k resistor.
For the moment, I haven't hooked anything up to 'the other side'.

I already found 1 error: I didn't connect the ENABLE pins to GND, which explains why I couldn't 'bleep' the two rows when the WAV trigger was connected. That issue is solved now, all the connections are made when I look with my multimeter. The board still cannot read the SD card, though. On the CLK pin I see a clean 24Mhz carrier, just as I would without the modification.
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I'm thinking that maybe the switch is not ready when the Sparkfun boots. De chips power supply is a 3.3V regulator that gets its input from the same power supply than the Sparkfun board. As the Sparkfun board only initialises its SD card during startup (it says in the manual that you need to power cycle the board each time the SD card is removed or re-inserted), would it be possible that the switch simply isn't ready fast enough? Does that make sense?
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I don't switch speed  would be the problem. Keep checking stuff.
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Allright, I've got it working. Apparently the wire I used to connect the GND from the Sparkfun to my 3.3V regulator causes too much induction. If I put the oscilloscope's ground pin to one end of the wire and the probe to the other end, it doesn't seem clean at all. With a shorter cable it still looks dirty but it seems to pass the treshold, because it works.

I assume this problem will be solved in a later stage where everything will be neatly fitted on a proper PCB with a ground plane.
Next step: integrating the VUB300 on the other end of the chip. I'm sure you'll hear more problems soon :-)

Thanks!
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Woo hoo!  Incremental progress - always a good start smiley-cool
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