Adding sensore


#1

I added a temperature sensor to the OpenROV. I used an LM35 which does 0 to 100 degrees C at 10mv per degree. The AtoD on the Arduino processor is 10 bit which gives you 5v/1024 or around 0.005 volts per count. So you have a resolution of about 0.5 degrees C. You need to remove R76 on the top of the Cape board and add R30 on the back of the Cape bd. This frees up ADC1 which is tied to 5v supply and then hook the 3 pins from the LM35 to 5v, gnd. and Pin 1 of Analog in. I hooked 5 volts and ground to J1 on the Cape bd. I drilled and taped a hole in the electronics tube end for a 1/8 inch pipe plug. I drilled out the brass pipe plug .1 inch and epoxy the LM35 into it. Then screwed in the pipe plug assembly and hooked up the wires. Using the new Open Cockpit code it is easy to send the temperature to the screen changing openrov.ino.

I also added a pressure sensor. I used an Omega PX40-100G5V which does 0 to 100 psi. This has 0.5 volt offset and goes to 4.5 volts or a span of 4 volts. So 25 psi is 1 volt or each count is around .12 psi. Figuring 15 psi for 32 feet in fresh water gives you an approximant depth. You need to remove R57 on the top of the Cape board and add R31 on the back of the Cape bd. This frees up ADC2 which is tied to 3.3v supply and then hook the 3 pins from the PX40 to 5v, gnd. and Pin 2 of Analog in. I again connected 5 volts and ground to J1 on the Cape bd. I drilled a hole in the electronics tube end for a small pipe nipple and used a small piece of tubing to connect the two. Using the new Open Cockpit code it is easy to send the data to the screen as depth.

I had both parts lying around from previous projects and they are both 5 volt parts which makes it easy to hook them up to the Cape board. The LM35 is pretty cheap, but the pressure sensor is around $60 US. I needed to trim the one end of the electronics tube structure to get everything to fit together. Now I just need to test it in the lake, but it is snowing today and in the mid 20’s F, so that will have to wait.

I really appreciate the new OPEN COCKPIT code!! I can play with the Arduino software but was not up to java script and all the rest.

John

1531-sensorandparts.jpg (59.5 KB) 1532-sensorsandelecend.jpg (178 KB) 1533-sensorsassembled.jpg (186 KB)

#2

Nice work! I'm excited to hear the results of the test (once you get to it through the snow) :D


#3

My building skills are better than my spelling....

I just got it back together and put it in my test tank. The area for the test tank is attached to my shop but not heated (look at temperature). There was ice on my test tank earlier this year.

Depth and temperature seem to work, at least in the tank.

I also switched back to 8 batteries as suggested and removed the inner tube. Reisnalled the ping ball balls which keep it neutral.

I wonder if a fin on the top would help it to go straight in the water???

John

1535-OpenROV2413182013.jpg (161 KB) 1536-testbottomtesttank.jpg (180 KB)

#4

Nice job John.

If I can't come up with a good I2C pressure sensor soon, I'll probably do something similar to what you did, using an amplified voltage-output sensor. I'm really hoping that the I2C pressure sensors by Measurement Specialties get into the distribution pipeline soon. But if not, I'm going to put an I2C auxiliary A-D converter on my ROV and will be able to read a pressure sensor that way.

I like that the Omega sensor you're using handles exposure to fluids- most of the sensors I've seen in this form factor are only rated for exposure to gases. It would be interesting to know what Omega thinks about putting salt water into the pressure port.

-W