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## misterhouse-users

 RE: [misterhouse-users] How to watch for a specific voltage with Weeder Digitial I/O board? From: Shane Harrison - 2003-11-26 09:33:48 ```I'm no great hardware engineer but I'd use a comparator. Take a look at: http://home.cogeco.ca/~rpaisley4/Comparators.html for example. Basic idea would be that you would feed the -ve input to the comparator with a reference voltage (the threshold that you want to detect). This could be done by a voltage divider. The +ve input would be driven by the line you want to detect the voltage on. If the +ve goes above the reference it switches the output on. If it is below, the output is off. Probably easier to run everything from 5V. Hence comparator supply would be 5 volts and your reference voltage as well. This would mean dividing down the input line with a resistor network so it never exceeded 5 volts. As example - say your input line had a maximum voltage of 20V. Use a resistor network to drop this to a maximum of 5V ie. 1/4. Clearly your thresholds would also be reduced by the same amount. Resistor voltage divider information should be easy to find on the net if you are new to that - or simply ask a few more questions. HTH Shane > -----Original Message----- > From: misterhouse-users-admin@... > [mailto:misterhouse-users-admin@...] On > Behalf Of Kirk Bauer > Sent: Monday, 24 November 2003 2:17 p.m. > To: misterhouse-users@... > Subject: [misterhouse-users] How to watch for a specific > voltage with Weeder Digitial I/O board? > > > Okay, you would think that with my degree in Computer > Engineering I could figure this out for myself, but I'm just > not very good with > electronics. I'm hoping somebody can give me a idea of what > kind of circuit I should build and then I can do the calculations. > > Sure, I could do this with an Analog input card, but not only > are those more expensive, but they have fewer inputs, and it > seems a bit overkill. Plus, I don't have an Analog input card > laying around. > > So, here are the three things I want to monitor: > > Garage door "safety sensors" (light beam to keep it from > shutting on something, as seen at the two terminals on the > garage door opener: > No obstruction: 6.17V, 20mA > Obstructed: 6.52V, 14.5mA > > Garage door opener light (I found that the voltage on the > terminal going > to the open button changes when the light is turned on, and > I'd like to > monitor this): > Lights off: 17.30V > Lights on: 16.26V > > Door sensor hooked up to alarm system: > Door closed: 2.97V, 2.96mA > Door open: 12.8V, 0mA > > So, I basically have one Weeder Digital I/O board. I have > three voltages I want to monitor. Each has their own ground. > Each has two > positive voltages representing the two states. > > So, how do I turn, for example, 16.26V into a 0V input to the > Weeder board and 17.30V into a 5V input to the Weeder board? > > I"ll accept an answer of 'just buy an Analog input board' if > that is my best option. > > Thanks for any help you can provide. > > -- > Kirk Bauer > http://linux.kaybee.org | http://www.autorpm.org | http://www.logwatch.org > > > > ------------------------------------------------------- > This SF.net email is sponsored by: SF.net Giveback Program. > Does SourceForge.net help you be more productive? Does it > help you create better code? SHARE THE LOVE, and help us > help YOU! Click Here: http://sourceforge.net/donate/ > ________________________________________________________ > To unsubscribe from this list, go to: > http://sourceforge.net/mail/?group_id=1365 > > > > ```
 Re: [misterhouse-users] How to watch for a specific voltage with Weeder Digitial I/O board? From: Gary Sanders - 2003-11-29 02:46:56 ```I agree that a comparator is probably the best way to go, and it's dead simple to build, but there's (at least) one 'gotcha' involved in using one for this particular application. The two voltage states to be compared in one case were fairly close together. One value was 6.17 volts, and the other one was 6.52. That's only about three tenths of a volt difference. If you aren't using regulated power sources for both the signal to be measured, AND the comparator power supply, you could easily have one or both power supplies drift to the point that the comparator window isn't where you originally set it, yielding results that are not what you expected in the long term. Especially if great care wasn't taken to ensure that the trip point isn't dead center between the voltage values. If the power supply for the signal to be measured isn't regulated, of course, as a workaround you could just use the same power source to power the comparator circuit. Then, as the signal source drifts, the comparator window would also drift in the same direction, and (hopefully) continue to work. Gary Sanders Shane Harrison wrote: > I'm no great hardware engineer but I'd use a comparator. > > Take a look at: > http://home.cogeco.ca/~rpaisley4/Comparators.html > for example. > > Basic idea would be that you would feed the -ve input to the comparator > with a reference voltage (the threshold that you want to detect). This > could be done by a voltage divider. The +ve input would be driven by > the line you want to detect the voltage on. If the +ve goes above the > reference it switches the output on. If it is below, the output is off. > > Probably easier to run everything from 5V. Hence comparator supply > would be 5 volts and your reference voltage as well. This would mean > dividing down the input line with a resistor network so it never > exceeded 5 volts. > > As example - say your input line had a maximum voltage of 20V. Use a > resistor network to drop this to a maximum of 5V ie. 1/4. Clearly your > thresholds would also be reduced by the same amount. Resistor voltage > divider information should be easy to find on the net if you are new to > that - or simply ask a few more questions. > > HTH > Shane > > >>-----Original Message----- >>From: misterhouse-users-admin@... >>[mailto:misterhouse-users-admin@...] On >>Behalf Of Kirk Bauer >>Sent: Monday, 24 November 2003 2:17 p.m. >>To: misterhouse-users@... >>Subject: [misterhouse-users] How to watch for a specific >>voltage with Weeder Digitial I/O board? >> >> >>Okay, you would think that with my degree in Computer >>Engineering I could figure this out for myself, but I'm just >>not very good with >>electronics. I'm hoping somebody can give me a idea of what >>kind of circuit I should build and then I can do the calculations. >> >>Sure, I could do this with an Analog input card, but not only >>are those more expensive, but they have fewer inputs, and it >>seems a bit overkill. Plus, I don't have an Analog input card >>laying around. >> >>So, here are the three things I want to monitor: >> >>Garage door "safety sensors" (light beam to keep it from >>shutting on something, as seen at the two terminals on the >>garage door opener: >> No obstruction: 6.17V, 20mA >> Obstructed: 6.52V, 14.5mA >> >>Garage door opener light (I found that the voltage on the >>terminal going >>to the open button changes when the light is turned on, and >>I'd like to >>monitor this): >> Lights off: 17.30V >> Lights on: 16.26V >> >>Door sensor hooked up to alarm system: >> Door closed: 2.97V, 2.96mA >> Door open: 12.8V, 0mA >> >>So, I basically have one Weeder Digital I/O board. I have >>three voltages I want to monitor. Each has their own ground. >> Each has two >>positive voltages representing the two states. >> >>So, how do I turn, for example, 16.26V into a 0V input to the >>Weeder board and 17.30V into a 5V input to the Weeder board? >> >>I"ll accept an answer of 'just buy an Analog input board' if >>that is my best option. >> >>Thanks for any help you can provide. ```