RF Transmitter

Thread Starter

byawire

Joined Jan 28, 2011
5
I am designing a circuit to detect when a constant feed paper roll has run out. I need 4 transmitters and sensors going to receiving location. The receiver and transmitters will be about 50 feet apart.
I was thinking of having an LED on one side of the paper and a LDR on the otherside. When the paper runs out it will sense the light, trigger the transmitter and light a display LED on the receiver. I guess I will need either a four channel receiver or run it through a microprocessor.

I haven't done any designing for some time so any assistance will be greatly appreciated.
 

bertus

Joined Apr 5, 2008
22,266
Hello,

What will be the distance between the 4 sensors with the transmitters?
If the sensors are quite close to eachother you could multiplex or encode the signals to one transmitter.

Bertus
 

gizmoman0

Joined Jan 21, 2010
26
Thinking about this I think you could do this with only one receiver and 4 transmitters, all set on the same channel I believe. If you had a 4 bit encoder on each transmitter and pull a unique bit high when that ream ran out, your receiving 4 bit decoder would correspondingly pull that specific bit high. So your data for each machine would spit out in general:

0001
0010
0100
1000

And having an led hooked to each decoder bit would let you know which machine was out. Think that would work?
 

Thread Starter

byawire

Joined Jan 28, 2011
5
There are photointerrupters made to do just that. There is a slot for the paper and an IR emitter and phototransistor.
I knew there must be an off the shelf switch for what I was wanting to do but none of my searches using photoresistor and LED came up with the correct name. This way the design and testing have been done. Much Thank this is definitely going to save a lot of setup time.

I was leaning towards the 4 bit encoder myself. Thanks for the validation.

Thanks for all the replies. I'll run the schematics by when I work them up, Hopefully I can still solder. Any recommendations on electronic suppliers. I ran across some small transmitters/receivers from Reynolds Electronics, does anyone have any experience with them.

Once again thanks to everyone for responding.
 

KMoffett

Joined Dec 19, 2007
2,918
Thinking about this I think you could do this with only one receiver and 4 transmitters, all set on the same channel I believe. If you had a 4 bit encoder on each transmitter and pull a unique bit high when that ream ran out, your receiving 4 bit decoder would correspondingly pull that specific bit high. So your data for each machine would spit out in general:

0001
0010
0100
1000

And having an led hooked to each decoder bit would let you know which machine was out. Think that would work?
Why not 2-bit? (assuming no transmission = no problem):
00
01
10
11

Ken
 

gizmoman0

Joined Jan 21, 2010
26
Why not 2-bit? (assuming no transmission = no problem):
00
01
10
11

Ken
You would have to add logic gates to the decoder output to figure it out which led to light.

I bought an rf kit and encoder/decoder set from reynolds or rentron.com I believe and they worked fine, but might be able to find the parts a bit cheaper somewhere else
 

KMoffett

Joined Dec 19, 2007
2,918
So your receiver has 4 independent outputs? Are the 4 transmitters coded for independent identification? Do you have a specific link?

Ken
 

gizmoman0

Joined Jan 21, 2010
26
The transmitters and receiver would all be on the same channel code. The photodetector would trigger the transmit enable and send the corresponding code for that device such as 0010. Then the receiver and decoder would turn on the correct led. The only problem I could see would be if more than one ream ran out at the same time the transmitters might fight and screw up the transmission
 

Thread Starter

byawire

Joined Jan 28, 2011
5

thatoneguy

Joined Feb 19, 2009
6,359
From how I read the 4 bit pack, it only included 1 Tx and 1 Rx. So you would need to order 3 more of These, might want to double check when ordering to be sure.

There is the possibility of collisions/lost data if two rolls run out at the same time, how likely is that?
 

Thread Starter

byawire

Joined Jan 28, 2011
5
I do realize I need to order a total of 4 transmitters I was just posting info on what I was planning ordering. I doubt anything will run out at exactly the same time but there is a possibility that they could run out near the same time. But we are talking minutes. I don't think lost data will be a problem with a 4bit decoder if I utilize all four outputs.
As far as color of the paper goes, it will be either white or brown. The core are usually brown. The core shouldn't be an issue if I use a photointerupter. I'm hoping it will work correctly with both color papers. I don't think it will be an issue.
 

thatoneguy

Joined Feb 19, 2009
6,359
As far as color of the paper goes, it will be either white or brown. The core are usually brown. The core shouldn't be an issue if I use a photointerupter. I'm hoping it will work correctly with both color papers. I don't think it will be an issue.
Core color won't matter with the interrupters, an edge of the paper only needs to be guided into the slot while loading a new spool, or a "swing away" arm to flip up once paper is in place.

The idea with the cores was an idea for "contact free", simply monitoring the light reflected by the paper spool, assuming a brown (dark) core and a light (white) paper, the out of paper condition could be signaled with a reflectance meter.

A reflective proximity sensor could be used in close (<1") to the running paper path though, even with black paper, eliminating any problems with "threading" a photointerrupter. The only requirement would be a lack of reflectance when the paper ran out. Similar theory, different way of using it. Not as reliable as interrupters, but a bit more hands off friendly.

I'm thinking like a lazy worker and trying to guess problems that might pop up is all.
 

Thread Starter

byawire

Joined Jan 28, 2011
5
I appreciate all of the input. It looks like I am going to order a few different types of sensor circuits and do a little experimentation to see what works the best. I'll post my results when I prototype it.
It seems like you have done quite a lot more of this than I have, any recommendations on suppliers. I'm just doing searches but have no experience in recent years with anyone.
 
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