7 replies to this topic

[KTF]

Hello,

 

I just purchased the netduino mini and this cable: http://www.amazon.co...=I1DDD2X9A6SVZH

 

I thought I should be able to get that to work but now I'm not sure.

 

Could anyone point me in the right direction?

[baxter]

The designation USB to RS232 is used loosely in product descriptions. It looks like your cable is USB to TTL. USB to TTL is NOT USB to RS232. Mini pins 1 and 2, COM2 (TX/RX) require RS232 logic levels. Pins 11 and 12, COM1 (TX/RX) are TTL. To check your cable, measure the voltage on cable TX; if it is + 3.3V or +5V then it is TTL. if 0V, then it is RS232. RS232 logic levels are inverted relative to TTL. TTL idles high, active low and conversely for RS232. If you have a TTL cable use it on COM1. Connections are cable TX to Mini RX and cable RX to Mini TX. I think there are different firmware versions for deployment on COM1 or COM2. I always use COM2 for deployment and COM1 for serial applications. See also, http://forums.netdui...x232-interface/

 

[KTF]

Got this working, thanks for the response, baxter! Cable worked perfectly. Loving the netduino... now I'm just having a hard time figuring ot how to write data that will persist after I turn it off and back on. (Like EPROM on the Arduino)

 

Any clues?

[baxter]

You could use an I2C EEPROM or FRAM. FRAM memory is fast like SRAM, but is non-volatile and retains data when power is removed. I have a proram in Visual Basic that uses a 8k byte FRAM, http://www.digikey.c...1175-ND/2766726 The program stores/retrieves data by name. It uses I2C code from here which is in C#,  http://forums.netduino.com/index.php?/topic/835-i2c-devices-using-the-i2cbus-class/?&p=6090&fromsearch=1 I simply added the storage by name mechanism to it. If you are interested, I can upload the program for you

[KTF]

Thanks for your response, Baxter!

 

I'm glad the answer can be a compact solution instead of something like an SD card reader - for my project I am needing to stay as absolutely light as possible; I will be logging data though, so the more memory the better- but it will only be for a few minutes.

 

I already am using a sensor on the I2C bus, but that should be fine since I would just attach the additional memory ICU to the bus. Do you think there would be a lot of overhead reading from the sensor, then switching the I2C bus to the memory ICU, writing, then switching back to the sensor, reading, etc? I would probably want to generate a data buffer I would fill before switching to the memory ICU and dumping the contents there.

 

I wanted to know the cons/pros of EEPROM vs FRAM, and I found this: http://www.ti.com/ls...P=FRAM&HQS=fram - It sounds very good. Especially since if I do switch between each peripheral frequently on the i2c bus, fast read/write times would be favorable- however, do you think with the netduino's speed it would even make a difference?

 

It looks like the FRAM is a bit more expensive than EEPROM options such as something like http://www.microchip...ocname=en010823 - however, with the benefits I am strongly leaning towards it. 

 

What are your thoughts? Are there any other considerations I should take into account?

 

Would these also work?

http://www.ti.com/ls...ts.page#p2084=1

[EDIT:] I just realized these are MCUs that *include* FRAM- are there any other places that carry FRAM memory other than digitech?

 

[EDIT #2:] Would these be compatible as well? Is there a reason you chose 400khz speed? 

Edited by KTF, 11 September 2013 - 01:29 PM.

[baxter]

Well, I don't think you would notice much overhead. As for 400 kHz, that is what was avaiable. These memory modules are really fast compared to an SD card. Mouser carries FRAM, but they seem to be more expensive than Digikey. Fujitsu also has a SPI FRAM, but I could not get it to work. It had something to do with latching the FRAM address during the SPI transaction. Cypress has a nvSram, but I can't see that it has any overriding advantage over FRAM http://www.cypress.com/?id=3489

 

The price for FRAM seems to be coming down. I paid nearly twice as much when I bought mine. Overall, I think FRAM is an ideal solution for secondary memory.

[KTF]

That seems like a great option, Baxter. Thanks again. I think I will go ahead and buy a module. I'm definitely interested in your code.

 

I know this post has morphed into something completely different- but I'm also interested in RF communication. Do you have any experience with that? I'm looking at something like this: https://www.sparkfun.../products/10154 or http://www.digikey.c...1654267?cur=USD , but I'm trying to find something that I will be able to use as a beginner- any recommendations?

[baxter]

There are a lot of options with RF. The thing that is most important is to pair modules from the same manufacturer to avoid headaches. Xbee  is is a nice expensive option. A cheap option is a pair of HC-05 Bluetooth master/slave SPP Transceivers,

http://www.ebay.com/...d=221158958927

You need a serial port at each end, COM1 on the Mini and a USB to TTL adapter on the PC or you can use these with an Android tablet if you install a serial APP.

 

Another option is a pair of Pololu Wixels. These are very versatile and well supported. I have a pair, but haven't used them much except for evaluation. http://www.pololu.co...og/product/1336. They almost take the place of a Mini, 15 user I/O lines, featuring 6 analog inputs, 2 USARTs (for serial or SPI), and 7 timer channels (capable of PWM). For functionality other than the supplied apps, it is necessary to do some programming in C, but they have a C compiler as part of the SDK.

 

The Ciseco RF modules are well designed and have reported communication of up to 1 km,

http://shop.ciseco.c...f-module-range/

http://www.ebay.com/...co-co-uk/m.html

http://www.techsupplies.co.uk/rfa030

These modules can be used to wirelessly program Picaxes because they have the ability to send a rarely supported break signal,

http://www.picaxe.com/docs/RFA021.pdf

 

Do a Google search on the Forum to see what others are using: 

 

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