HUD Project Update

ScubaDadMiami

Pretty amazing stuff you have done there.

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Howard Packer
IANTD CCR Instructor
Miami Beach, Florida
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Scuba_Vixen

OK, ... Now it's ready to squeeeeeeze into it's housing. (well, after I trim up the wiring bird's nest)

I kept thinking there was something missing, and I realized that it was having the A/D result available for quick easy calibration. .... So I added the little LCD. What's nice, is that with the LCD to show the A/D result, ... It can also show the PO2 to 2 decimal places, though it can't show the decimal point itself. (For PO2 less than 1.00, it shows leading zeros, so there's always 3 digits displayed ...ie; 021 for air)

That gives 2 totally seperate circuits, with seperate batteries, and the ability to check the HUD indication to the digital display of the circuit that drives it, and to the hi-rezolution digital readout.

Physically, the hi-res digital display board sits above the controller board on the right, and the LCD sits above the controller board on the left. The batteries are in their respective locations, and you can see the reed switches (there's 2, ... 1 for each circuit, one above the other) on the controller board between the battery connectors. "Magnet present" turns it all Off. (magnet present at the top of the hi-res display board to turn the backlight on) I've also put all the voltage regulator circuits on the controller board instead of on the seperate board.

In the pics, the 1st one is showing cell #1 (1.00 PO2) Notice that all the HUD leds are on. That's an "led test" feature that occurs at exactly 1.00 PO2 so when I calibrate, I also have a display check.

The 2nd pic shows cell #2 (1.14 PO2) .. You can see the center led for OK and the LO led both on, indicating OK, but a little low.

The 3rd pic shows cell #3 (1.26 PO2) .. You can see the OK and HI leds on, showing the PO2 is OK, but a bit hi.

I can make a quick change of 1 line of code to select my setpoint choice of 1.1, 1.2, or 1.3 ..... The display is set for 1.2 in the pics.

You can also clearly see 2 yellow leds, (between the OK and hi and low leds) ..... These are the leds that flash to indicate what cell the LO-OK-HI leds are about to display.

Overall, I'm wayyy happy with how it's turning out. If I change anything, I may change the display code to flash the HI and LO leds for very Hi or very Lo PO2's, but that's the only thing I can think of.



Darlene

Gibbon

Darlene,

It looks fantastic.

Perhaps today you should get it to say and flash
"Happy Birthday to you Happy Birthday to you"

:-)

jknights

Looking good
Cant wait to see it in its housing and ready to go u/w.

jknights

Darlene,
Looking at the latest pictures of the HUD.
You have two displays for the pO2.

Do we need a new circuit diagram for those of us who are less good at electronics ;-)

What is the technical specs/source/partnumber of the single LCD display with all the pO2 readings?

Thanks

Genesis

That's a 2x16 LCD - since its being driven by a Basic Stamp I assume the part is from Parallax (although there are a lot of places you can get those, and more than a couple where you can get the serial interfaces that go on the back of them.)

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Scuba_Vixen

I'm not sure, but are you referring to the schematic that I posted a good while back......

If so, that's not the schematic to this bit of kit.

That schematic was for a simple HUD that would monitor a dedicated cell, and could be built without a microcontroller.

This one uses a Parallax Basic Stamp2 microcontroller and monitors 3 cells sequentially, and blinks dedicated yellow leds to tell you which cell is being displayed. The lcd is also from Parallax.

Since calibration is done in hardware, having the result of the analog to digital conversions makes it quick and easy to calibrate it right on the money. That's why I added the 2X16 lcd (2 lines by 16 characters) display. Figuring the PO2 and displaying it on the top line is just a matter of a few lines of code that divides the A/D result by 25 and displays it. (explanation below)

The 4 digit numbers on the lower line are the A/D result for each cell. That number is in millivolts, as it's the output from the op amp amplifier stage. (it's a 12bit adc with a 4.096 ref voltage)

To calibrate, with the cells in 100% O2, set the op-amp gain trimmers so that the A/D results each read 2500. The 25 turn gain trimmers can match up to cell outputs over a wide range of base values. (nominally, cells with about 7 to 13 mv in air outputs)

The display with the 3 lcds, is a totally seperate circuit from the HUD controller/display, that is used to monitor the same 3 cells. If one circuit fails, or it's battery dies, the other is unaffected. It's basically the same as a Mark Munroe 3 display PO2 meter. Redundancy is good, and there was room in the housing. That display gets calibrated at the same time as the HUD controller, with it's own calibration trimmers.

There were actually 2 real reasons why I added the Mark Munroe type display:

One was that I wanted to see an accurate display of all 3 cells, simultaneously. That way I can compare readings in real time. ...... The HUD display reads and displays each cell sequentially, and takes about 8 seconds to scroll thru all three. That's not a big issue at a relatively constant depth, or when all is generally well. But when one cell is reading high or low, you want to see what the others are reading, *Right Frickin' Now*, .. not in a few seconds from now. When acsending or descending, and PO2 is changing more rapidly, I want all 3 cell readings live and in real time.

Secondly, concern over how long a 9v battery will drive my HUD leds was my other reason to include the seperate 3 lcd display. If the HUD battery runs flat during a dive, I still have a high accuracy readout for each cell to finish the dive.



Darlene

jknights

Darlene,
Thanks for the update.

Do you have pictures of the unit housed yet or are you still dry testing ?

I guess that the PIC code would also be useful. I'm starting to think that I would really like to build one of these HUDs so it is a question of making sure that I get get all the bits in one place before I build.

I'll probably need to contact you and get a shopping list and the PIC code. It might be good also to maybe get a new circuit diagram so I can wire up just like yours.

specopsintl

Darlene,
Why didn't you go with a three Tri-Color LED set-up? It seens like with the LED arrangement you have now that it would be rather confusing having to note what's going on with the light show. Uderwater, you want to reduce task loading as much as possible. Having a simple arrangement or 'this Single LED, is for this Single O2 sensor'. It may make it more easily understood, or allow faster reaction time. For example Red is Low, Orange is OK, Green is High. Flashing faster vs slower for degree of bad, Ok or good.


Steve

Scuba_Vixen

There's a couple reasons why I didn't use 3 tri-color leds.

#1, From a practicality perspective, 7 conductors in a cable gets to be pretty stiff. Jaw fatigue and ease of head movement are major concerns, especially as runtimes increase. 5 conductors is the most I found in a cable size practical for a HUD display, .... at least for me. For a no-neck grizzly bear sized guy, maybe welding cable wouldn't phase them.

The other reason has to do with "what works for me" visually. Different layouts seem to appeal to the way different people's brains work. I seem to click with the "left to right movement = increasing" perception mode.

That's why I put the LOW led on the left and HI on the right. With the display in the horizontal tube layout, it almost makes no difference what color it is, as the meaning is easily discernable by relative position in the display tube.

The last issue I had with 3 tricolor leds is that depending on what colors you have, not that there's much choice, (yellow or orange with red and green) telling which color is showing is not always so easy, depending on the water. This may be a somewhat individual thing as well. I know my eyes are not as young and focussed as they were a couple decades ago.

There's a post with a video clip of it in operation, it's really simple and intuitive to pick up what the display is telling you. With the horizontal tube mounting, it's also easy to rotate it a few degrees in the mount to get just the right intensity for the water conditions by rotating the tube, thus changing the viewing angle of the leds.



Darlene