Well, by emptying the silos, i mean the control system will follow the following sequence of operations :

1) A Batch needs 150KG from SILO-1, 200KGs from SILO-2, 600KGs from SILO-3 and 100KGs from SILO-4. This requirement will be transmitted to the uC Board by a computer over a serial (RS-485) link.

2) The uC board will Enable the solenoid(s) for pneumatically operated piston(s) to open Gate(s) / Chute(s) of SILO-1, and start measuring the weight in the hopper. (There are 2x gates on each silo, each individually controlled for Fast and slow discharging).

3) Once the required weight is achieved, it will close the gate / chute,

4) It will repeat the process for all the remaining SILOs untill the materials for a complete batch are in the weighing hopper.

5) uC will then activate the solenoids for Pneumatically operated piston to open gate of hopper to empty total contents on a conveyor.

Apart from all this, the uC is also controlling the Conveyor (ON / OFF), Vibrators for SILOs and Hopper (2 vibrators on each SILO).


I hope this description makes the scenario clearer.

For your question regarding the obsolete part, well, the final board may not have that part. Right now, at the testing stage, we have a lot of these parts lying around, so the initial test boards will be based on them. This also lets us be sure that a code which will run on this BASIC garden variety part will definately run on any other improved / newer part.

For the multi-channel ADC, well it could be used IF the system was being designed as a one compact unit. However, we want to try with different makes / brands of Summing amplifiers as well. Also, the setup already in place at my friend's place has load cells from Avery and these terminate on a Summing amplifier (this amp is a Chinese model, but very accurate. It is using OP07 opamps from Analog Devices).

The point is, the original system was based on a PLC and was designed and shipped from some Chinese OEM. My friend was having a lot of variance batch-to-batch - this was one problem.

Another issue was that the recipes needed to be changed on a daily basis for producing different products on the plant... with the OEM system this was very cumbersome.

NOW, that the OEM system has developed some faults in it and not working anymore, my friend was considering going for a re-development of the system, possibly on a custom control system with a computer front-end software that can store different recipes in a database, so the production guys can just recall the recipe of choice and send it to the control system for production.

There are a lot of other factors too, warranting a complete system re-design, but they are mostly of a Business-nature and so i have been kept away from them.

Initially, i am tasked with using the existing Load-cells and summing amplifier module on the system, and only developing the uC-board and computer system. But since i had doubts on the summing amp (its showing its age) and a few measurements didnt quite give the desired results, i though of developing the summing module too, if possible. If not, then off-the-shelf ones can be procured from market.