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A/D display for older vehicles

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I want to take the outputs from the various sensors of an older engine (1960's... pre CANBUS) and display them on a computer screen.

If I understand correctly, I think I need the following:
1) physical connections of the engine sensors to:
2) an analogue to digital converter.
3) a physical way to get the digital signals into the PC. (USB or serial)
4) software code that will translate the digital signals to something a computer can understand and present on a display
5) a user-interface that will allow for organizing, labeling and adjusting the various readouts.

Everyone I talk to makes this sound ridiculously simple. Comments like "just buy a $20 A/D" are like telling me to buy a light bulb when I need to read in a darkened room... hardly what I would call an end-to-end solution. :)
I expect it's all shelf-ware, but I expect also that there are a lot of wrong decisions to make.
Thanks in advance.
Ohhh... and I want it simple.
How many channels do you need? How many samples per second per channel do you need? How much money can you spend? A USB scope may do what you want.
Most likely you would need to start with modern electronic sensors for engine temperature and oil pressure. The volts and amps would be fairly strait forward. The fuel gauge would most likely need a circuit to adapt its variable resistance into some proportional voltage that a A/D converter could use. The speed would be able to be referenced off of a common cruise control sending unit which just puts out a set of pulses as it rotates and would fit in where every your speedometer cable hooks up to the transmission.

once everything is putting out simple variable voltage signals its a matter of how fancy of display you want to make.

Its doable but not exactly simple. Putting in the sensors would be the easy part. programming a display system that works properly with all of those signals could be a very long and frustrating process even if you have off the shelf software to work with.
Hello Canadian! I'm from TO and living in DC now on a big old boat. A assume a channel is an individual device? Probably 6 devices on each engine. The vessel is fully operational and things don't happen very quickly. The biggest concern would be overheating. If exhaust temp was monitored every couple of seconds, that would be more than adequate. How much do I want to spend? Not much. How much will I need to spend?
Are you just wanting to monitor the various sensors and sound an alarm if any of them reach a critical or possible engine damaging level? If so, you probably don't need a computer or ADC at all. Especially if it is an old system with all analog sensors.
I only want to monitor (and log?) engine and transmissions operating conditions. Coolant temp, oil pressure, drive oil temp, volts dc, exhaust temp.
Speed is off the GPS and always slow. I'm anticipating taking a long voyage in a year or so and I want to be able to get this ironed out before that.
This is one site among many that I think might have some of what I need. I don't understand a lot of the nomenclature and although they try, they aren't exactly retail-friendly. Weeder Technologies RS-232 Data Modules
The problem with offerings like this is that it might be more of a "black box" than I can use at sea. In other words, I want to build it so I can fix it if need be.
There are already alarms, but they are attached to one big bell. That's only for coolant temp and oil pressure. By the time the engine coolant alarm sounds on these, it's too late. I want to be able to set the alarm points and add sensors. I might also add a monitor to the water intake flow, so I 'd like to have a certain user control. Also, I have a couple of old Mil-Spec pc's with daylight-viewable displays. I have my GPS and weather instruments connected and if I can get the engine instruments hooked in, I'll be happy.
Unless you already know how to write programs for the PC, it cannot be both simple and cheap. I suspect that you won't find a pre-made solution that does what you want either. It sounds like it would need to be a custom job which would be exorbitantly expensive unless you DIY.
I would consider getting a microcontroller development board - you can get one for < US$30, comes with power supply regulator, RS232 interface (to connect to a PC serial port) chips, probably some LEDs (and other features you may not need) - then at least you have the hardware ready to program, then you just need to connect the sensors (& protection/filtering); if you ask nicely someone could probably help with the software/firmware. Be sure to get a dev board that has a bootloader or on-board programmer also.
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