Sonde drawing too much?

I am working on integrating an EXO2 sonde into the Smart Mooring system using a DCP Signal Output Adapter (to spit out RS-232). Here are the specifications for the instrument using this adapter…

  • Supply Voltage: 9-16 VDC
  • Current Draw Adapter: ~20 mA typical (@12VDC)
  • Current Draw Sonde: ~sleep 0.25mA reading and 100 mA during operation
  • Max Net Current Draw for Systems: ~120 mA (@ 12VDC)

I wired the sonde/adapter to the dev kit and the V was fluctuating between 12 and 11 V at a 1 second interval and the sonde was not taking readings. I then removed the adapter’s power and ground wires from the dev kit and wired them to an external battery and everything was working fine. I also tested the dev kit’s V-OUT and ground without anything wired in and the V was as expected and stable.

Does that mean the sonde is drawing too much for the dev kit and I have to rely on external battery power for the sonde?

Hey there, it might be helpful to see a wiring diagram of your total system so we can get a full view of what’s going on. A photo might suffice as well if we can easily see the pin outs…


Is this helpful?

Cobi, I’m sorry I lost track of this post…

Something that might be helpful is to use the power monitor referred to in the RS232 integration guide under the section “Physically integrate the sensor”

There’s a few key elements of this tool that we’re still working hard to document more thoroughly:

hope this helps!

Power monitoring

The Bristlemouth Development has two different INA232 power monitor ICs that monitor voltage and bi-directional current.

0x41 / D65 - measures power flowing into Port 2 of the Mote. This power goes to the Mote, the Bristlemouth Development Board, and through the Mote to any downstream consumers.

0x43 / D67 - measures power delivered to 5V and Vout (9-19V) rails on the Bristlefin (Dev Board). Note - measured at the 24V level.

These are controlled in the firmware by **sensorsPollIntervalMs**More information can be found in Guide 5:

Bristlemouth Dev Kit Guide 5: Developing a Simple Application

Some notes about the current implementation of this:

  • The accuracy is about +/- 0.5mA.
  • The Bristlemouth Mote orientation matters.
  • The default hello world app will consume about 150mW.
  • Currently there is no simple way to distinguish the Bristlemouth ports on the Development Board.

Here’s an example of the power monitor:

Powering from Port 1 - no power is measured:

power | tick: 26209, rtc: 0, addr: 65, voltage: 23.929600, current: -0.000250

Powering from Port 2 - ~160mW is measured:

power | tick: 22209, rtc: 0, addr: 65, voltage: 23.929600, current: 0.006750

Adding this here as well in case it’s helpful.

If we want to test whether or not the load is causing the issue we can put a power resistor in place to simulate a load.

@evan recommended a 50 ohm power resistor with a 10W rating, like: HS10 50R J Ohmite | Resistors | DigiKey.

Using the 12V Vout output, you should get 240mA / ~3W of power dissipation in the resistor which is 2x the expected power of the Sonde and should be no issue for the dev board when powering off of wall wart or Spotter. We’d recommend trying the wall-wart first and then the Spotter (with full batteries).

Please note that the resistor will get hot to the touch. Don’t put it on or near anything flammable.