# SPI to USB converter Question (for STM32F105)

I have a question regarding which SPI to USB connector to choose and what the main difference is between them. All i want to to is monitor the SPI activity going on which is possible through an SPI port connection on my board.

There are two USB to SPI convertors I have seen:

Why is the price difference so big between them?

• You want to monitor it or control it? – Samuel Mar 27 '15 at 19:46
• Only monitor output. No controlling. The control is all don't by the arm processor – user2464665 Mar 28 '15 at 1:58
• Then you want a logic analyzer, not a USB to SPI device. The difference there is observation vs control, respectively. – Samuel Mar 28 '15 at 2:19
• would a logic analyzer interpret USB messages? I am looking to send text data that the ARM outputs over a USB COM port – user2464665 Mar 30 '15 at 1:44
• Yes, check out the Saleae Logic device. It can interpret SPI, USB, and many others. – Samuel Mar 30 '15 at 1:50

From the Aardvark page it comes complete with:

Aardvark SPI Host Adapter Unit
6 foot USB A->B cable
Windows USB Drivers
Linux USB Hot Plug Configuration files
Rosetta Language Bindings: C/C++, C#, .NET, Python, Visual Basic
Examples
Datasheet
Documentation


Plus it is a finished product and they will even customize it with your own logo for you in order to promote your own brand. I'd say those are some pretty significant value added features.

The Sparkfun item is for hobbyists and is only provided as-is. You are pretty much expected to know (or to learn) how to use it by yourself. The software for it is all open source.

It seems those are the largest differences. The Aardvark requires a minimum order of 100 items.

• totally true. I've used the AArdvark (it was spi and i2c) at work in a professional environment. It is very robust, the programming libraries are amazing. great documentation. Besides SPI it can do standard GPIO (like how you would do on a microcontroller). Its basically a very well polished version of the sparkfun with A LOT more featureS A LOT more stability and A LOT bigger price tag – andrew Mar 27 '15 at 20:20
• I've found the C# libraries for the MCP2210 to be very complete. It also has GPIO and it's even cheaper than the Sparkfun device. – Samuel Mar 27 '15 at 20:39
• I can buy a single aardvark unit. But is the frequency at which it samples important? The spark fun one is 750Khz vs the aardvark which is 4Mhz – user2464665 Mar 28 '15 at 2:00

I use the USBee SX for this task. While more expensive than either option you link to, it supports capture of up to 8 signals, and has decoders for SPI, I2C, Async UART and other protocol, as well as an API for writing your own protocol decoders. Decoders are applied to signals, and you can have as many enabled as you need. This helps immensely when debugging activity on more than one communications channel. Their BusBee module is similar, but with only 4 signals captured it really can't handle more than one bus at a time.

At SparkFun, also take a look at the Bus Pirate. It handles more protocols than just SPI, and is based on an open source PIC that could be reprogrammed to suit other uses as well. It is popular for its flexibility.