Engine room monitoring

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Engine room monitoring

#1 Post by LJK » 16 May 2020, 07:53


Am sketching out the design of a system to gather engine data and transmit to helm position and would appreciate advice on a couple of points (choice of ADC and PSU).

Currently using a nodeMCU 8266 running ESP Easy to gather (via 1-wire) temperature data and tansmit via MQTT to an rPi running OpenPlotter for display. Want to add 4 other analogue channels (gearbox oil pressure and fuel pressure).

Sensors attached to the engines will be simple pressure transducers.
Voltage: DC 5V. Output: 0.5-4.5V linear voltage output. 0 psi outputs 0.5V, 250 psi outputs 2.5V, and 500 psi outputs 4.5V.
Unsure of sensor’s power requirements, but this entry “Load Resistance: ≤ (supply power-6.5V/0.02A)Ω” from the sales literature suggests to me they will pull a max of 0.02amps each.
Need an offboard ADC to get 4 ADC channels. Appears from browsing that either ADS1115 or PCF8591 might work.


What’s the best ADC for the role?

PSU: the boat’s power is a highly variable 11-14V. Given the sensors need 5V appears to me that a 5V rail could power the 8266 via VIN and also power the sensors.
Am I okay running the NodeMCU at 5V?
My browsing suggests an LM2596 might suit? The engine room gets very warm, so the PSU needs to temp tolerant (while stuck inside an unventilated box).

thanks, LJK

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Re: Engine room monitoring

#2 Post by TD-er » 17 May 2020, 23:38

LM2596 is a fine DC-DC converter.
However you must have a look at how much effect some voltage ripple may have on the analog signals you try to measure.
The LM2596 itself does operate at a relative high frequency, so I doubt it will have much effect.
LM2596 can deliver up to 3A, but please take a good look at the datasheet for the right value for the coil to match the required current range at the expected voltage drop.

The NodeMCU boards have a linear voltage regulator (AMS1117) on board to turn 5V into 3v3 so you can also power them via USB.

I can't tell which of the mentioned ADCs will be best for your purpose.
I've seen the ADS111x being mentioned more often, so I guess that one is being used more in projects.

Just make sure you can use the same ground for all analog sensors.
If not, then you may need to consider using multiple nodes each measuring a single value and then using the p2p controller to share their values among nodes in your network.

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