Advanced EOL/EOLR Hacking

jeditekunum

Active Member
This thread is for any EE or advanced hobbyists here...
 
I have a situation where I have some 3.3k EOL installed in nearly impossible to access locations and I want to change to a different panel brand. Most panels are in the 1-2k range.
 
One option I am considering is the Bosch B Series that uses 1k EOL. The documentation outlines 3 voltage ranges that the panel recognizes:
 
0-1.3v
2-3v (normal)
3.7-5v
 
There is no suggestion that the voltage seen is ever over 5v.
 
Does anyone know how inputs are typically wired internally? Is it a Constant Current Source or just a dumb resistor divider network?
 
Depending on the details (where all the devils are) there may be a way to put another parallel resistor at the panel to convert my 3.3k setup to look approximately like a 1k would - ie still maintaining the voltage ranges for supervision.
 
 

ano

Senior Member
jeditekunum said:
This thread is for any EE or advanced hobbyists here...
 
I have a situation where I have some 3.3k EOL installed in nearly impossible to access locations and I want to change to a different panel brand. Most panels are in the 1-2k range.
 
One option I am considering is the Bosch B Series that uses 1k EOL. The documentation outlines 3 voltage ranges that the panel recognizes:
 
0-1.3v
2-3v (normal)
3.7-5v
 
There is no suggestion that the voltage seen is ever over 5v.
 
Does anyone know how inputs are typically wired internally? Is it a Constant Current Source or just a dumb resistor divider network?
 
Depending on the details (where all the devils are) there may be a way to put another parallel resistor at the panel to convert my 3.3k setup to look approximately like a 1k would - ie still maintaining the voltage ranges for supervision.
OK couldn't post for a bit.
 
I can't speak for all systems, but the Omni Pro uses a constant current source, with a pretty basic 8 bit A to D converter. You could decrease the current so it would work with a higher resister, but then you are risking more noise/lightning problems. 
 

jeditekunum

Active Member
It will be awhile before I have to time to work on this but I think I'll acquire a Bosch and give it a try.

By my calculations 1600 ohms across the inputs at the panel will bring a 3300 ohm EOL into the correct voltage range for the Bosch panel (which specifies 1000 ohms). I'll try this with 1500+100 resistors in series.

My calculations say normal state will then be ~2.7v and cut wire will be 4v.

Even on paper it is rather critical to get the right value. For example, with 1470 ohms (1k+470) it would be only ~3.6v for a cut wire and that is out-of-spec for Bosch. It's possible the 1600 may need to be tweaked a bit more for cable resistance, etc.

I'm making a bet here that all/most panels are a constant current source as that seems to be the most rational design. The Bosch is a relatively inexpensive bet to make.
 
OK couldn't post for a bit.

I can't speak for all systems, but the Omni Pro uses a constant current source, with a pretty basic 8 bit A to D converter. You could decrease the current so it would work with a higher resister, but then you are risking more noise/lightning problems.
I have a specific question(s) on this topic.
- Does each zone input have its own A/D converter?
- Is each zone a 2-input A/D? Or are there single input with a common ground?
- If it is common ground, is the "-" lead the common?
- The older (smaller) Omni LT had a common terminal for each group of two inputs. So this design had to be single input with common ground. But was the design on the LT different than its larger brother? or was it the same design?

Just thinking out loud.
 

ano

Senior Member
I see two analog multiplexers on the zone expander board, so I'm 99.9% sure its multiplexed. You know, those 8-bit A/D cost a lot back then. There is an 8 pin chip on the board, which I can't read, and that is likely the 1-channel A/D converter. I'm sure there was a common for all the zones, but can't remember if its + or -.
 

RAL

Senior Member
I see two analog multiplexers on the zone expander board, so I'm 99.9% sure its multiplexed. You know, those 8-bit A/D cost a lot back then. There is an 8 pin chip on the board, which I can't read, and that is likely the 1-channel A/D converter. I'm sure there was a common for all the zones, but can't remember if its + or -.
This sounds similar to what the Elk M1 does. The microprocessor on the M1 board has a single A/D converter, with a built-in 8-to-1 multiplexer. This can be expanded to up to 18 channels through the use of an additional multiplexer, external to the processor. Elk takes this approach to provide 16 zone inputs on the main board. I haven't checked the zone expander boards, but assume they are similar. All the inputs share a common signal ground.
 
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