LimeSDR Mini GPIO Connections

The place to discuss the use of the LimeSDR Mini for amateur TV applications
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M0YDH
Posts: 155
Joined: Sat Dec 31, 2016 5:59 pm

Re: LimeSDR Mini MUST READ Information

Post by M0YDH » Sat Feb 02, 2019 9:32 am

Hello Dave
In light of what you report on the calibration routine, would it be a good idea to put a small co-ax relay after the Lime mini?
E.g https://www.minikits.com.au/electronic- ... -relay-kit.
It could have a 50 ohm dummy load or SMA termination on the NC line and be switched to NO by the Lime PTT GPIO pin. It's a 5V relay. I think I would forget to turn the power amp on at the right moment.

May we have a schematic of your test board and another picture showing the wiring to the GPIO pads from the other side of the screened enclosure to that shown on the Wiki? I didn't understand the Lime mini GPIO pins information on the RF Myriad site. Sorry.

The article and interview in Lime news is very good.
https://limemicro.com/community/the-bri ... F2AMd9WvVI

Many thanks for all your hard work

73
David M0YDH

G8GKQ
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Posts: 1257
Joined: Sun Mar 22, 2009 1:21 pm

LimeSDR Mini GPIO Connections

Post by G8GKQ » Sat Feb 02, 2019 10:28 am

Hi David

The LimeSDR Mini GPIO connections are arranged in 2 vertical rows, adjacent to the screened can.

If you hold the board with the USB connector on the left and the SMA connectors on the right, there are 4 vertical rows of 5 connections. The right hand 2 rows are the FGPA GPIO connector, J5. The layout of the pins is:

Code: Select all

Pin Func  Pin Func
1   GPIO0   2   GPIO1
3   GPIO2   4   GPIO2
5   GPIO4   6   GPIO5
7   GPIO6   2   GPIO7
9   GND     10  +3.3v out
I have allocated GPIO 0 to Band D0 (brown wire), GPIO 1 to Band D1 (orange wire), GPIO 2 to band D2 (yellow wire) and GPIO7 to the PTT (green wire). I have also connected Gnd (black wire) and +3v3 out (red wire). Photo below.

The test board has 4 BC108s with their emitters grounded. The bases are connected to the GPIOs through 4K7 resistors and the collectors have 470R resistors connected in series with them and the LEDs which are powered from the board's 3.3v supply. Note that this is only a low current supply and would not drive a relay! In fact I would be tempted to use an opto-isolator if you were driving anything other than an indicator LED to avoid blowing up the LimeSDR FPGA. Or just continue to use the Raspberry Pi GPIO output - it still works and is cheaper to replace if you blow it up!

Your suggested relay solution would work, but looks a very expensive solution to a simple problem. Suitable surplus relays of similar spec go for £15 maximum at rallies. Or you could consider switching the Porstdown RF output switch (if still in use) to an unused output instead?

Dave
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Lime GPIO.JPG
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G0EID
Posts: 21
Joined: Thu Oct 17, 2013 3:19 pm

Re: LimeSDR Mini GPIO Connections

Post by G0EID » Sat Feb 02, 2019 12:23 pm

To prevent accidents on the bench and save soldering wires directly to the LimeSDR board.
I fitted some 1.27mm headers and a cable out to 0.1” breakout board.
LimeSDR-Mini_GPIO.jpg
LimeSDR-Mini_GPIO.jpg (607.16 KiB) Viewed 1307 times
73
Dave

M0YDH
Posts: 155
Joined: Sat Dec 31, 2016 5:59 pm

Re: LimeSDR Mini GPIO Connections

Post by M0YDH » Sun Feb 03, 2019 8:07 pm

Thank you to both Daves
Stuck indoors with a cold, I used the chance to start learning KiCAD and sketched the attached schematic. I hope I understood the written instructions. ;)
Adafruit.com wanted between $15 and $32 postage on $8 of parts to do the breakout board, connectors and cable. I got them from the Pi Hut and similar on Ebay for £15 post free.

all the best

David M0YDH
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Lime Mini Indicator board.JPG
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G8GKQ
Site Admin
Posts: 1257
Joined: Sun Mar 22, 2009 1:21 pm

Re: LimeSDR Mini GPIO Connections

Post by G8GKQ » Sun Feb 03, 2019 8:12 pm

Hi David

The circuit is correct. Well done.

Dave

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