Can it be done and with what? Suggestions greatly appreciated

jasonmartin1313@hotmail.c

Previously I have worked with the MOBO2PE with color sensors and serial outs for a robot. I have a new project that might push my knowledge, and patients, to the max. I need to tie into a digital weight scale. It has a serial rs232 output of the total weight. I need to set up an alarm contact that will activate once a set weight is met. To set preset weight I want to use a keypad and have the set and current weight dispayed on a small LCD. does this sound realistic? can it be done with a stamp or prop? The second part is I would like to incorporate a remote display perhaps even a remote keypad at some point, all wireless. I want to concentrate on the intial goal at first. Any feed back/suggestions are so welcomed. I wanted to use a small plc but the price isnt realistic when you add in serial/touch/display it comes out to more than a new scale cost. Note that this is on an industrial scale.

StefanL38

I have never worked with a basic stamp. So I can't tell if a basic stamp can do it.

A propeller-chip surely can do all of this.
best regards
Stefan

Duane Degn

I agree with Stefan, this is a piece of cake for the Prop.

I use several digital balances almost everyday. They communicate with a Propeller and the data gets displayed, logged transmitted wirelessly.

You may need a RS-232 to serial chip. I've used the DIP version of this one several times. SparkFun used to sell the DIP version of the chip. I bet there are still places where the DIP version is available.

I read on the forum that if you're just receiving the RS-232 signal you don't really need the converter chip but I haven't tried this myself.

Do you know how the data is formatted coming out of the balance? The two balances I have each use a different format. One outputs a bunch of additional numbers besides the weight so I have the code wait for specific characters. When these characters are identified the Prop knows to treat the data that follows as the weight.

While none of the tasks you mention will be hard for the Prop, program to the Prop to do all these things is not trivial (particularly for one new to the Prop).

rwgast_logicdesign

Maxim will sample out max3232 which can do Rs232 to 5v, and 3.3v TTL signals, making it compatible with a bs2 or prop. All you have to do is register at maxim's web site using a real e-mail address search for for max3232cpe and request a sample. Although I have never thought about it I suppose Duane is right, you should be able to receive serial signals without the chip. The chips primary function is that it has a built in charge pump to boost the out going signals to +12v/-12v. When you are just receiving you could run the PC's TX line through a resistor divider to cut the voltage down. Here is a good article on dealing with mixed voltage communication:

http://www.savagecircuits.com/forums/content.php?309-Mixed-Voltage-Systems-Interfacing-5V-and-3-3V-Devices

It is not directly related to rs232 but the circuits shown could be adapted in this scenario and are much easier to set up than a max3232 chip.

kwinn

If you only need to receive the serial data from the scale a resistor and 2 diodes are all you require. The series resistor limits the current and the diodes limit the voltage swing to one diode drop above the supply and below ground.