teensy and arduino pro mini i2c

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berathan90

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Hi I managed to make a dj mixer using teensy 3.1 . Now I am going to make 4 turntables on side of it .Brain of my device is inside mixer box. However since I am making them with separate boxes I would have to use alot of wire to send data from turntable decks to mixer box (where teensy-brain- is located). I came up with an idea, using i2c connection. However I wont need that amout of pins in turntable decks to make a master teensy and 4 slave teensys. (i need 4 analog pins and 10 digital pins) .also 4 times 20 $(each teensy cost approximately 20 $) is kind of expensive. So I am planing to buy 4 arduino pro mini put them inside the decks and connect them to teensy 3.1using i2c connection .Is this possible? Does this thing make sense ? Or do you have another option? I am up to all opinions.
Thank you very much
 
Well it should work. Note, for the pro-mini you will need a programmer to down load to the card, so if you don't have one (or an Uno you can wire up as a programmer), be sure to figure that cost into the equation. You only need one programmer for all of the cards.

Also note, that on the Pro mini, the i2c pins are on the inside of the chip, and not along the outside row which might be problematical, depending on if you are using breadboards or perf-boards. I would think about the Nano instead of the Pro Mini, since it has a USB port for download, and being a ATmega32u4 (Leonardo or Teensy 2.x) chip, the i2c pins are on pins 2/3. You would want to run whatever you get at 3.3v, so you don't have to do any level shifting.

I've been thinking about making some of the ATtiny85 chips I bought work for i2c devices that have a single analog device.

I'm not sure whether you need digital inputs, digital outputs, analog, and/or PWM devices. If you need just digital input or outputs, consider an i2c break-out card like the MCP23017 (16 input/outputs) or MCP23008 (8 input/outputs). For example from Adafruit: https://www.adafruit.com/products/593. However, if you are only buying a few of these, the UPS shipping cost from Adafruit is likely higher than the chips, but still 4 MCP23008's + shipping is still cheaper than a Teensy 3.1.
 
Which pro mini should I buy 3.3 volt or 5v. I know that teensy 3.1 is capable of 5v. Pro mini 5v has a high mhz crystal than 3.3 volt. should I go with 5 volt module or 3.3 volt module?
 
They are basically the same form factor and pin out and functionality; you're preference as to voltage. I prefer the 3.3 V Pro Mini since I work with 3.3 V sensors mostly. Neither is in the same class as the Teensy 3.1 when it comes to pin functionality and processor speed. My advice is to invest in the Teensies and learn how to use them; they are only a few dollars more.
 
You want 3.3v. While the Teensy is 5v tolerant, the signalling from the Teensy is still 3.3v. Now, it may happen to work if the Pro mini sees a 3.3v signal, but just to be sure, it is simpler if both chips are running at the same voltage.
 
onehorse said:
They are basically the same form factor and pin out and functionality; you're preference as to voltage. I prefer the 3.3 V Pro Mini since I work with 3.3 V sensors mostly. Neither is in the same class as the Teensy 3.1 when it comes to pin functionality and processor speed. My advice is to invest in the Teensies and learn how to use them; they are only a few dollars more.
Click to expand...

I will already use a teensy. However for a one teensy 3.1 I can get 10 pro minis. Because I would need at least 5 teensies.
 
MichaelMeissner said:
You want 3.3v. While the Teensy is 5v tolerant, the signalling from the Teensy is still 3.3v. Now, it may happen to work if the Pro mini sees a 3.3v signal, but just to be sure, it is simpler if both chips are running at the same voltage.
Click to expand...

Thank you very much. I am going with 3.3 v pro mini. However I am going to purchase one nano v3. Also I wont need and ttl usb chips cuz I have a genuine arduino uno I can programme minis with it.
 
berathan90 said:
Which pro mini should I buy 3.3 volt or 5v. I know that teensy 3.1 is capable of 5v. Pro mini 5v has a high mhz crystal than 3.3 volt. should I go with 5 volt module or 3.3 volt module?
Click to expand...

My first thoughts are around how you plan to use the devices and what your performance requirements are - based on that, a couple thoughts that might drive you to a particular device/configuration:
- What type of processing will the devices (in particular the slaves) be required to perform? Neither a 5V/16Mhz or 3.3V/8Mhz pro mini will be able to accomplish nearly that of a Teensy 3.1 but I am not clear on whether a mini is suitable for your processing needs or not.
- Are you running distances beyond a couple feet between the master and slaves? At moderate to high data transfer rates I've had trouble with 3.3V I2C over a couple of feet w/o a driver of some sort - if you want/need the option of long runs consider adding a line driver - most that I've used are reasonably priced (1-3$ - and you could order samples if you just want to test out the design) - they might come in SOIC packages but with a breakout board you can easily solder them.
 
Note, in terms of performance, i2c is a relatively slow protocol (and as digitalCowbody says, it is not really geared for long distances).
 
onehorse said:
How many of them work reliably?
Click to expand...
you will never know :D
No for real, even in sparkfun bad parts may come. This is not relevant to money that you pay it is the luck that you have. Thus I had a good laptop, unfortunately first device that I got was broken , so they had to replace it. By the way % 100 of my orders are okay from ebay, dx, or other online shops. However the build quality cannot be compared with teensy of course but still it is a cheap option than teensy.
 
I only caution that I have received bum boards from China and all attempts to get a refund or exchange parts were ignored. I had to cannibalize them for parts. Whereas Sparkfun has cheerfully and promptly replaced boards and components I have had the least question about. I hope all your Pro Minis work well!
 
This is an Arduino Pro Mini. It uses ATmega168. They cost 18,50 € (same as Teensy 2.0)
ArduinoProMini_Front_3v3.jpg


What you linked to is
Free Shipping! 10PCS/LOT Pro Mini Atmega328 3.3v 8MHz For Arduino Compatible nano uno
Free-Shipping-10PCS-LOT-Pro-Mini-Atmega328-3-3v-8MHz-For-Arduino-Compatible-nano-uno.jpg_250x250.jpg

with no data sheet except for a mention of the procesor, who knows what that is.
 
MichaelMeissner said:
Note, in terms of performance, i2c is a relatively slow protocol (and as digitalCowbody says, it is not really geared for long distances).
Click to expand...

Well...that stuff is often repeated but one has to really look at the details. I've made myself for my own purposes a little board (14mm x20mm) with a PCA9600 I2C buffer chip on it to drive some FM+ capable I2C slaves (a PWM chip) from a Teensy 3. I've done so successfully at the FM+ speed of 1MHz over 5m. It still showed crisp signals on the oscilloscope at 1.5MHz. The Teensy 3.1 is able to do run the I2C bus at up to 2.4MHz.

I currently am operating an LED system with 11 I2C devices on approximately 5m of CAT 5 cable (preconfigured with RJ45 plugs and sockets) using a Teensy++2 at 400KHz. That's about the limit for that specific application as I can see on my oscilloscope.

As it applies to this project max 400KHz are possible with the Atmel processors, depending on cable length. And to get good signal over distance 5V is recommended in many application notes from NXP and others for best signal to noise ratio. That's what the PCA9600 does beautifully as it also works as a I2C level converter for e.g. 3.3V to 5V.

Another thing to look at is whether the Application really needs digital and analog outputs at each turntable deck. If only digital I/O is needed then a I2C multiplexer instead of a Arduino Pro Mini may be all that's needed.

One should also mention that the Teensy 3.1 has two(2) separate I2C busses, so if data transfer needs to be fast then not all four turn tables have to share one I2C bus but can be split.

I can only advise not to get this CCC (Cheap Chinese Crap) from ebay and buy the product from Sparkfun.
 
Sparkfun.com is temporarily OUT OF STOCK!!

This a 3.3 V 8 MHz Pro Mini. It uses the ATMEGA 328P AVR processor; there might be some look alikes that do use the Atmega 168, but not the ones from Sparkfun. You can get these (and I have) for $89.60 per ten and they are worth every penny. I use them by the dozens (ok, maybe two dozen) and they are absolutely reliable and high quality. Furthermore, Sparkfun will answer any question with a smile and they bend over backwards to help all, especially newbies (I know). Nevertheless, the Teensy 3.1 is in an entirely different class compared to the Pro Mini, and it too is well worth the money at twice the price.
 
Okay everybody thanks for your advise. I changed mind I will order 1 nano and 1mini from sparkfun.(sparkfun shiping is kind of expensive) And get 1 clone nano and 1 mini. That makes 4 :) .Buying 10 pieces of unknown board is kind of risk as you all said. However 3 $ is not much for to give it a shot. Thanks :))
 
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