Resistor ladder assistance please

[jsguitar93]

I am trying to create a ladder of resistors that is connected to a set of buttons where when pushed (by themselves or in combination) will give me different voltages (which will then be measure by a micro controller). I need 16 combinations in total. I am currently using the attached circuit, I am using a dip switch with 8 channels to attempt the 16 channels, but I can't get to 16 without weird combinations (problem). If anyone can think of a way to fix this with my current setup I would be very happy, but if you have a better idea (circuit, switch, etc) please let me know.

http://s46.photobucket.com/user/rocker_j_batman/media/image.png.html?filters[user]=14513887&filters[recent]=1&sort=1&o=3

http://s46.photobucket.com/user/rocker_j_batman/media/image.png.html?filters [user]=14513887&filters[recent]=1&sort=1&o=3

here is the setup

http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2356.jpg.html?filters[user]=14513887&filters[recent]=1&sort=1&o=0



http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2357.jpg.html?filters[user]=14513887&filters[recent]=1&sort=1&o=1

http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2356.jpg.html?filters [user]=14513887&filters[recent]=1&sort=1&o=0

http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2358.jpg.html?filters[user]=14513887&filters[recent]=1&sort=1&o=2

http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2357.jpg.html?filters [user]=14513887&filters[recent]=1&sort=1&o=1

http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2358.jpg.html?filters [user]=14513887&filters[recent]=1&sort=1&o=2


all the pins on one side of the dip are connected together acting as the hot rail (green wire).
The yellow on the bottom is ground, and the last green wire which is at the same node as the last resistor is the v out with is being measured by my micro cont. with respect to ground.

There are some combinations that are almost exactly the same (1,2 = 5) that I would like to use, but they are so close even the micro (which reads to the thousandths place) can't tell them apart.

Thanks

Jonathon

 

[berkeman]

I am trying to create a ladder of resistors that is connected to a set of buttons where when pushed (by themselves or in combination) will give me different voltages (which will then be measure by a micro controller). I need 16 combinations in total. I am currently using the attached circuit, I am using a dip switch with 8 channels to attempt the 16 channels, but I can't get to 16 without weird combinations (problem). If anyone can think of a way to fix this with my current setup I would be very happy, but if you have a better idea (circuit, switch, etc) please let me know.

http://s46.photobucket.com/user/rocker_j_batman/media/image.png.html?filters[user]=14513887&filters[recent]=1&sort=1&o=3

http://s46.photobucket.com/user/rocker_j_batman/media/image.png.html?filters[user]=14513887&filters[recent]=1&sort=1&o=3

here is the setup

http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2356.jpg.html?filters[user]=14513887&filters[recent]=1&sort=1&o=0



http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2357.jpg.html?filters[user]=14513887&filters[recent]=1&sort=1&o=1

http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2356.jpg.html?filters [user]=14513887&filters[recent]=1&sort=1&o=0

http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2358.jpg.html?filters[user]=14513887&filters[recent]=1&sort=1&o=2

http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2357.jpg.html?filters [user]=14513887&filters[recent]=1&sort=1&o=1

http://s46.photobucket.com/user/rocker_j_batman/media/IMG_2358.jpg.html?filters [user]=14513887&filters[recent]=1&sort=1&o=2


all the pins on one side of the dip are connected together acting as the hot rail (green wire).
The yellow on the bottom is ground, and the last green wire which is at the same node as the last resistor is the v out with is being measured by my micro cont. with respect to ground.

There are some combinations that are almost exactly the same (1,2 = 5) that I would like to use, but they are so close even the micro (which reads to the thousandths place) can't tell them apart.

Thanks

Jonathon

Welcome to the PF.

The photobucket links don't work for me. Have you looked at how regular computer keyboards work, including the x-key "rollover" mechanisms (that's what let's you press several keys at a time and still decode them correctly without "ghosting")?

http://en.wikipedia.org/wiki/Rollover_(key)

 

[Baluncore]

You need an R-2R ladder. The 2R resistors are connected to either the input reference voltage or to ground.
http://en.wikipedia.org/wiki/R-2R_ladder#R-2R_resistor_ladder_network

 

[Baluncore]

http://www.play-hookey.com/analog/analog_and_digital/d2a_converter.html

 

[alphy]

Thank you for sharing your circuit and setup, Jonathon. It seems like you have a good start on your resistor ladder. However, I can see why you are having trouble getting to 16 unique combinations. It looks like you are using an 8-channel dip switch, which would only give you a maximum of 8 unique combinations. In order to get to 16, you would need a 16-channel dip switch or use multiple 8-channel dip switches in parallel.

Alternatively, you could also consider using a digital potentiometer instead of a dip switch. A digital potentiometer is an electronic component that can function as a variable resistor and can be controlled digitally. This would allow you to have more precise control over the voltage output and give you more unique combinations.

Another option is to use a multiplexer or demultiplexer. These components can help you switch between different resistors in your ladder to create different combinations. This would require some additional circuitry, but it may give you more flexibility in creating your 16 combinations.

Overall, I would suggest exploring these alternative components and seeing which one works best for your specific application. I hope this helps and good luck with your project!