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Postby Dave » Thu Oct 05, 2017 8:55 am

BMS Doug wrote:The MyPiFi GPIO expander board gives you 16 channels of I/O which could be 5V tolerant (Dave can you confirm?)


That's correct, the MCP23017 IC when powered via 5v allows for 5v tolerant I/O. There's no risk of damage to your Pi due to how the I2C lines work.

Since these io expander chips use i2c to communiate, you can theoretically power them from 5V while still connecting the i2c data lines to a 3.3V device like the pi. That's because the Pi has two i2c resistors that pull up SDA/SCL to 3.3V. Just make sure not to connect any resistors to SDA/SCL to 5V and you can power the chip from 5V (and have 5V input/output on the MCP chip). Its also fine of course to power the MCP chip from 3.3V but the 5V line on the Pi has more current capability so you might find its better to go that way.

Source: https://learn.adafruit.com/mcp230xx-gpi ... -it-all-up

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Postby BMS Doug » Thu Oct 05, 2017 9:00 am

Dave wrote:
BMS Doug wrote:The MyPiFi GPIO expander board gives you 16 channels of I/O which could be 5V tolerant (Dave can you confirm?)


That's correct, the MCP23017 IC when powered via 5v allows for 5v tolerant I/O. There's no risk of damage to your Pi due to how the I2C lines work.

Since these io expander chips use i2c to communiate, you can theoretically power them from 5V while still connecting the i2c data lines to a 3.3V device like the pi. That's because the Pi has two i2c resistors that pull up SDA/SCL to 3.3V. Just make sure not to connect any resistors to SDA/SCL to 5V and you can power the chip from 5V (and have 5V input/output on the MCP chip). Its also fine of course to power the MCP chip from 3.3V but the 5V line on the Pi has more current capability so you might find its better to go that way.

Source: https://learn.adafruit.com/mcp230xx-gpi ... -it-all-up


Yes, I was wondering if the MyPiFi board I linked was fed from 5V or 3V3?

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Postby Dave » Thu Oct 05, 2017 9:01 am

BMS Doug wrote:
Dave wrote:
BMS Doug wrote:The MyPiFi GPIO expander board gives you 16 channels of I/O which could be 5V tolerant (Dave can you confirm?)


That's correct, the MCP23017 IC when powered via 5v allows for 5v tolerant I/O. There's no risk of damage to your Pi due to how the I2C lines work.

Since these io expander chips use i2c to communiate, you can theoretically power them from 5V while still connecting the i2c data lines to a 3.3V device like the pi. That's because the Pi has two i2c resistors that pull up SDA/SCL to 3.3V. Just make sure not to connect any resistors to SDA/SCL to 5V and you can power the chip from 5V (and have 5V input/output on the MCP chip). Its also fine of course to power the MCP chip from 3.3V but the 5V line on the Pi has more current capability so you might find its better to go that way.

Source: https://learn.adafruit.com/mcp230xx-gpi ... -it-all-up


Yes, I was wondering if the MyPiFi board I linked was fed from 5V or 3V3?


Ah yes, it is indeed fed from 5v :)

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Postby dariosm » Thu Oct 05, 2017 4:06 pm

BMS Doug wrote:Arduino have Wifi or Ethernet modules available to convert your project to stand alone.


A pre-configured breadboard should be able to handle the necessary adaptions, the circuits are pretty simple and the components fairly cheap. there aren't a lot of different configurations needed.


The Raspio Analogue Zero will sit on top of a Pi Zero and give you 8 channels of analogue inputs.

The MyPiFi GPIO expander board gives you 16 channels of I/O which could be 5V tolerant (Dave can you confirm?)

Both of the above boards can be made up on solderless breadboards with very cheap components and easily googled instructions.
8 channel 5v tolerant I/O - MCP2308 £0.84ea (cheaper in multiples)

ADC chips vary in price depending on number of channels and resolution (number of bits) you only need 2 channels at most for any single sensor, An 8 bit ADC will convert the analogue signal into one of 256 discreet digital values, 10 bit gives 1028 discreet values. Arduino use 10 bit ADC but as low as 8 bit should be sufficient for demonstration purposes.
The MCP3002 is 2 channel 10 bit ADC £1.46ea (cheaper in multiples)


So, even when sensor from the mentioned kit, connected through simple circuits on a breadboard to the Rpi is one way to go, there are (IMHO) two simpler approaches:
- Arduino board + connectivity shields,
- Rpi board + gpio expansion hats (analog inputs and 5v tolerant gpio's).

I should also mention that we're looking for cheaper solutions, than the one completly self contained Grove Pi provides. Grove is clearly simpler and plug and play, but expensive.

BTW, I'm visiting Southampton in november to meet a friend at the University of Soton. Later on back in Argentina, we will give the IoT lecture to kids from the senior college year, hoping to provide them the tools to experiment and make their own projects. That's why I'm looking forward to find the most electronics agnostic and simplest approach (if you allow me the expression), so students can focus only in the IoT general concepts and eventually the code.

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Postby BMS Doug » Fri Oct 13, 2017 9:04 am

dariosm wrote:So, even when sensor from the mentioned kit, connected through simple circuits on a breadboard to the Rpi is one way to go, there are (IMHO) two simpler approaches:
- Arduino board + connectivity shields,
- Rpi board + gpio expansion hats (analog inputs and 5v tolerant gpio's).

I should also mention that we're looking for cheaper solutions, than the one completly self contained Grove Pi provides. Grove is clearly simpler and plug and play, but expensive.

BTW, I'm visiting Southampton in november to meet a friend at the University of Soton. Later on back in Argentina, we will give the IoT lecture to kids from the senior college year, hoping to provide them the tools to experiment and make their own projects. That's why I'm looking forward to find the most electronics agnostic and simplest approach (if you allow me the expression), so students can focus only in the IoT general concepts and eventually the code.


Note that for both Arduino and RPI solutions some of the sensors would still need additional components on a breadboard. as previously mentioned.

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