Why are these devices so expensive (> $700)? (http://www.dataq.com/products/hardware/di710.htm). Especially the ones that have an Ethernet interface. I searched the forums and noticed people have tried to make one themselves using micro controllers like PIC32 (http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2607).

Is it better to buy a used netbook for about $200 and interface the cheaper USB based devices for about $50 (http://www.dataq.com/products/startkit/di148.htm). The netbook can then be connected to the network using the Ethernet port to send the data upstream to the control room.

 

They are expensive because they serve a small niche market. They do not benefit from economies of scale which bring down manufacturing costs. They may actually save an integrator enormous amounts of time and money over doing it any other way. It all depends on the needs of the guy with the checkbook.

 

for home use a cheaper model will be fine - it will have less of the bells and whistles of a full-featured (eg. expensive) model but should suffice for home use.

what is your application, and requirements?

 

They are expensive because they serve a small niche market. They do not benefit from economies of scale which bring down manufacturing costs. They may actually save an integrator enormous amounts of time and money over doing it any other way. It all depends on the needs of the guy with the checkbook.

Makes sense.

 

for home use a cheaper model will be fine - it will have less of the bells and whistles of a full-featured (eg. expensive) model but should suffice for home use.

what is your application, and requirements?

I am planning to make a control room to monitor pH, EC/PPM and temperature of the nutrient solution for growing Aeroponic plants in a farm. Since the solution will be kept in a tank in the middle of the farm and will be subject to forces of nature (extreme temperatures, humidity, etc) I wanted to send the data to a temperature controlled room in the farm to record the data.

The control room should also have options to start and stop water pumps circulating this nutrient solutions to the plant roots. The ON and OFF should be controlled by a computer.

Since USB devices have to be close to the host computer they are not an option. Using ethernet based devices provides an option to have the probes located far away from the control room.

 

I am planning to make a control room to monitor pH, EC/PPM and temperature of the nutrient solution for growing Aeroponic plants in a farm. Since the solution will be kept in a tank in the middle of the farm and will be subject to forces of nature (extreme temperatures, humidity, etc) I wanted to send the data to a temperature controlled room in the farm to record the data.

The control room should also have options to start and stop water pumps circulating this nutrient solutions to the plant roots. The ON and OFF should be controlled by a computer.

Since USB devices have to be close to the host computer they are not an option. Using ethernet based devices provides an option to have the probes located far away from the control room.

there are extenders made for USB devices (essentially repeaters) which allow chaining of lengths of USB cable up to 150 feet - they are pricey though


http://www.cablestogo.com/product_list.asp?cat_id=1521

you could also run the control wires and probes/sensors the long distance and keep the USB controller close to the host PC.

You could also look into a wireless data transmit/receive.

These all sound pricey, and likely are - but there are a lot of angles to take to tackle this.

How are you planning to control the pumps and valves? PLC? uC and custom PCB?

 

We used to make greenhouse controllers around a 6809 computer and custom interface boards. It should be feasible with a modern microcontroller.

 

there are extenders made for USB devices (essentially repeaters) which allow chaining of lengths of USB cable up to 150 feet - they are pricey though...

I thought of having long running cables to the probe and keeping the USB device next to the computer in the control room. But then the long cables will introduce a lot of noise in the readings.

I was going to use the digital I/Os in these devices to drive a relay to power the motors ON and OFF.

Looks like this is going to be an expensive project either in terms of money spent in buying a device or tons of time spent in trying to make one myself. At this point buying a device seems better than trying to reinvent the wheel myself.

Using a used netbook to send data from the USB device to an Ethernet cable sounds attractive as well. Unless the extreme summer heat melts the netbook to a lump of plastic!

 

generally speaking unless you are trying to personally gain or learn something go with an existing solution.

its proven, and if it doesnt work you greatly reduce where you are searching for problems and debugging.

best of luck, dont be afraid ot ask for more help.

be careful with the I/O and relay matching as well.