HUD Project Update

Scuba_Vixen

Well, actually my leccies are ....

My electronic modules are all nicely potted and ticking along perfectly.

The housing is ready for some final exterior finishing to dress it up a bit and drill and tap for the connectors.

The one for the hud display is connected temporarily for testing, and the wires for the cell input connector are visible.

There's enough room to use either standard 9V batteries, or NiMH batteries as in the pics.

As you can see, I had to redo the triple display board (from the previously pictured design) to relocate the calibration pots between the screws that secure the lid. The cal pots for the hud controller are below the screw thread depths, so no issues there. Standard 1st stage regulator port plugs will be used for the cal port plugs.

Now I'm really getting excited to be diving it soon.



Darlene

rdmmdr

darlene

great clean unit. but the next one that you build why not try software caibration saves have to put ports in for the pots. i include a two step high low cal with a voltage limit for weak cells to auto fail. if you want to see the code email me off list and i will send. ps the oopic compiler is free so you can view the source. and if you use the oopic pic you get seven channels of a/d built in. the complier work in vis basic, c, and java for those of use who dont like learning new code. i liked your use of the 16x2 dispalys but i wanted mopre data at hand so went to 20x4 dispaly the heads ended up as 6x3 inch block. did you include a heart beat indicator some thing flashingonce per code cycle, if the pic freeze up the display will not refresh.

i am trying in the pressure pot next week an of the shelf co2 cell electrolite based co2 sensor. i expsect to see some problems with o2 saturation but that should only be a software fix after i get the call table right.while it will not work like the temp sticks it should pick up channeling. the cell should solve the problem of lens failure in the ir dectectors due to pressure. and since i am use i biopak scrubber the temp stick idea will not work for me. i figured since ohsa new rules came out might as well try to comply. if anyone has tried and failed with the figaro 4160 sensor give me a shout before i go through the gas to try and make it work.

rick miller

sven

Rick,
Have you found some information on how the 4160 performs in the presence of other gases (like He)? I am by no means a specialist, but from the reading that I have done it appears that these sensors ae extremely sensitive when it comes to mixed gases and require some sort of continuous calibration (via program code) with the changing ppHe, ppO2. Big challenge!

At the moment, I am working on a HUD for my Inspiration myself (partially inspired by Darlene's pictures on RBW a while a go - Thanks Darlene!). The addition of a CO2 sensors would be very welcome.

The response time of the 4160 is given as 2min to 90% of final value. I take it this is the initial warm up. But how much does it trail a change in ppCO2 in the ambient gas?

Reading through the spec sheet: The code would have to be more elaborate than for O2 sensors, as the delta EMF drifts and also works on a logarithmic scale. The Figaro 4161 draws much less current (250mW compared to the 1.25W of the 4160), and appears a better candidate. Is there any reason why you chose the 4160?

One more question: Which PIC do you use and why (compared to others)?

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Sven

The Sydney Project website: http://www.sydneyproject.com
My Blog: http://sven.rebreatherworld.com

"Whenever you find yourself on the side of the majority, it's time to pause and reflect." Mark Twain

rdmmdr

sven

I chose the "oopic" pic for my first unit because the others had to use strap on a/d converters at the time, and since the basic code is over 15 pages long. I did not plan on changing platforms for the new one. I chose the 4160 because of the warmup time being about 5 mins as opposed to 2 hours for the 4161. And yes the ppo2 enviroment will effect the sensor how bad i dont konw yet, however since we are looking at the same rise in pp of co2 it might not be a problem, and a correction table can be used. Would not wwant to try with a scr but with limited set point of a ccr it might work. Will need to see what the pot data says. while the sensor wanders it is stable for the time period we will be looking at with an air cal. and the 4160 has a thermistor built into it for temp compesation.

rick m

Scuba_Vixen

You can definately tell if the microcontroller locks up.

The controller sequentially reads 3 cells and displays the result for ~2.5 seconds each on the HUD leds. Towards the end of each ~2.5 second display interval, there are 2 yellow leds that flash, once, twice, or 3 times, indicating what cell is about to be displayed next by the red/blue/red PO2 indicating leds. .... No flashing yellows, ... there's a problem.

As a backup, the 2X16 display is programmed to write characters at 50ms intervals. If you watch that display, you can see each cell's portion write to the screen slowly enough to be observed every 2.5 secs or so. ..... No visible rewrites, ... there's a problem.

If I find myself building another unit, I'll probably go with software calibration. I'd also put the batteries in a seperate compartment from the main. The current design allows the use of the simplest of the basic stamp2 controllers. It's also half or less, the current draw of the more sophisticated modules with memory on board. The less times I have to take the cover off, to swap out batteries, the better overall reliability will be.

Also, since coding isn't my forte, I thought adhering to the KISS principle the first time around was best.



Darlene

rdmmdr

darlene

the coding is not bad for a software cal the math is simple use a air offset point for the sensor and a 100% offset point. the pain is the hex dec conversion for the screen but once you get used to that it is easy.
good luck with the new one. parts have to wait for the weekend will be geting wet in montery this weekend expect cold water and shit vis with the stroms but what the hell.
rick m

bobmaggi

Has anyone tried using a OLED for a display unit yet? The currrent draw is less than a LCD with backlight since it produces its own light and it can come in colors.
I'm planning on using one for my next project along with SMT PICs as to reduce the overall size of the circuit down to a minimum and use fiberoptics for a HUD - the actual LEDs would be housed in the controller box as to eliminate a leak point.

Bob

Genesis

I'm considering doing fiber optic for the HUD to go with the controller.. it has its advantages. For display only it works well; for comms its potentially problematic since you need power on both ends.....

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jknights

That's a great idea and I'm sure that Darlene could add that into the PIC as the code could be quite small. I have some flow charts of what is required to do the checking of pO2 and in fact I was thinking about making an O2 injector to make a eCCR but gave up as I didn't have time and my Inspiration does it all anyway. I wanted to use it in my Submatix conversion from SCR to CCR but I have made the Submatix a M-CCR unit with a Hydrogom valve. Very easy conversion.


Rick, Regarding the use of a gas CO2 sensor the common thought process is that the latency is too high and that an electrochemical or some other method is required e.g. measure temperature front like APD do with Vision electronics.

In fact I was talking to Martin Parker of APD today at London Dive Show and we were discussing this CO2 monitoring and the need for a real time pCO2 output. His view is that it is too costly but I suggested to him that it is sufficiently worrying to Rebreather divers that he should investigate cost to build and do some market research as I believe that a £500/$800 unit would sell like hot cakes !!

jknights

Darlene,
Have you got the unit all potted and diving yet?.

Would love to see some dive ready photos of the unit.

Thanks