Hi, I am looking for microcontroller PIC by Microchip or Arduino having 140 plus I/O for temperature/humidity monitor. There are solutions with external serial/parallel chips and external multiplexers but it's not so easy to find compact solution for which we don't need to make a big PCB. I appreciate if you have any suggestion in selecting Microcontroller with 130 plus I/O.

 

Where are these 140 sensors located? (how far apart?) Is it reasonable to have all of them wired to one microprocessor? That seems unlikely to me.

 

Find a suitable FPGA and implement a soft processor inside the FPGA. You would need a small 8-pin serial flash memory to hold the processor implementation so the FPGA could initialize itself on powerup. You would need to adapt whatever open source design you choose to be able to address the 140 I/O pins. This would be a challenging, but hardly impossible project to embark upon. Additionally, the maintainability of such a project would be difficult to ensure IMHO.

 

I've used the MCP3008 IC for 8 x 10 bit channels of A/D. I particularly like it because it's available in thru hole and the 8 channels are pins 1 to 8, i.e. down one side. I've used four together for 32 channels but 140 is a bit of a stretch! If I was trying to get 18 ICs into a compact space I'd bend the pins to "spread eagle" them and sandwich them between two pieces of strip board with all the A/D lines on one board and all the power/control lines on the other board. If soldering, you need to get this right first time. With an Arduino UNO you will be short of I/O for chip select so (at least) one 4017 decade counter IC should help, the rest coming from available Arduino I/O lines.

 

Let us say you need to connect to 200 or more sensors.
What kind of data are the sensors supplying? Is the data 1-bit, such as ON/OFF? Is the data analog voltages or digital n-bit?

One solution is to use multiplexers. You do not need to wire all 200 signals to the MCU. For example, a keyboard has 104 switches. A piano has 88 keys. The keys do not have individual connections to the MCU.

 

What kind of data are the sensors supplying? Is the data 1-bit, such as ON/OFF? Is the data analog voltages or digital n-bit?

140 plus I/O for temperature/humidity monitor.

 

My question still remains. Is it analog, serial or parallel data input to the MCU?
Temperature/humidity monitoring does not need Input/Output pin on the MCU.
The hardware solution will depend on the nature of the data stream. Also distance to each sensor is important. Is it monitoring temperature/humidity in a hotel, manufacturing plant or a greenhouse? We don't know.

 

In any case, 140 wired inputs is not the way I would do it. It is bound to be unwieldy.

A better solution would be an IOT node for each sensor.

 

I can’t imagine hanging 200 sensors off the GPIO of an MCU.

One wire bus, or SPI, or a serial option, or Ethernet but GPIO? That doesn’t seem like it would ever be a good idea.

Am I missing something?

 

We had to do it with 256 electrodes on an EIT experiment (EIT = Electrical Impedance Tomography).
Here is an example with 32 electrodes.

 

We had to do it with 256 electrodes on an EIT experiment (EIT = Electrical Impedance Tomography).
Here is an example with 32 electrodes.

256 connections to a single MCU without expanders? What has that sort of GPIO?