SPG Recommendations/ DIY LP Inflator Hoses? / New ppo2 monitor

Bnscherm

What is the general consensus regarding SPGs?

1. Mini "Button" style pony gauges.
2. Two normal SPGs
3. Verify before you dive that you have enough gas, and don't bother taking SPGs
4. Some other combination

Also, I've dove my homebuild enough now to feel the need for clean/custom hose routing. I need some unusual length LP inflator hoses to do this. Is there a source for reusable hose ends; I'm likely to need a new hose length each time I make a mod?

I'm working on a compact PPO2 handset to replace the bulky panel meter version I'm using now. It's less half the size. I looked into the Picaxe chips that Tom Rose mentioned, and came up with a digital PicAxe design for monitoring ppo2, but I'm still convinced manual O2 addition is the way to go. Still waiting on some smt components before I can get it in the water...

I found some GREAT multi conductor cable as long as I don't run into noise problems. It's listed on McMaster as "continous flex" cable. Is very flexible and is much more durable then the SJOOW cable I've been using.

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Corallaro

For PPO2 monitor you can see this:
http://www.rebreatherworld.com/home-...p-down-12.html
and, about your code, wich resolution of ADC do you use?
and, nice your housing but, which type of battery you use?
Giovanni

Bnscherm

Giovanni, looks like we have some similar ideas.

I'm using an OpAmp in conjunction with the Picaxe's internal 10-bit ADC. The prototype code running in the picture is only operating at 8-bit, and the resolution appears to be adequate. I know there has been a lot of talk about what resolution is needed, but it seems these applications have been for the solenoid controller. With 8-bits and the gain calculated for a full-scale voltage at 2.55 ata that gives me .01 ata per step (well, not quite since I have some voltage headroom for sensor deviation) More resolution might be nice but I don't really think it's necessary for this application, or am I missing something?

I'm currently using a RCR132A 3.6V battery for my HUD that I have mounted inside the scrubber. I plan to add a second cell to the scrubber, and run the handset at 7.2V. Freshly charged batteries will need to be used prior to each days diving.

A magnetic switch inside of the handset keeps the display turned off until it is removed. The procedure will be to purge the loop with O2, and then remove the magnet which will turn on the display, and calibrate the O2 cells. This eliminated the need for any buttons/holes in the display.

Corallaro

Hi Bnscherm

we have arrived at same conclusion about the resolution of ADC

you can see my code and electric scheme on previou posts of the thread started by Tom Rose..

http://www.rebreatherworld.com/home-...p-down-11.html

for the moment i prefer decide when calibrate pushing two buttons, i also use one of them to change the setpoint and disable hud

i use a reed normally closed to on/off the circuit and other reed for backlight

is most important the control of battery level, if the level is down the reading of ADC is not correct!

probably, but i don't test it, with the picaxe 28x1 or 40x1 with the command "calibadc" we can solve this problem

other important element is to use a rail-to-rail precision op-amp, i use an AD822 but a my friend in other circuit have used an OP291

can you share your scheme and code?

for picaxe only the code of "Dave-Rite v 3.51",the initial code of Tom and my code are shared

Giovanni

Woz

Easiest way of making custom length reg and inflator hoses is to buy some long reg hoses and chop them off to the length you need, screwing on an AP or SAP reusable reg-end fitting. For the inflator end, get hold of one of those Scubapro inflator things that screws onto a standard reg hose and turns it magically into an inflator hose.

__________________
Still punting shiny diving tatt to gullible divers
www.kitfondle.co.uk

Bnscherm

I haven't tested my circuit with a wide variety of battery voltages, but with a low dropout voltage regulator for the power supply I don't think this should be a problem. As long as the batteries aren't reaching there drained state where the available current is below the circuit requirements, the reference voltage for the ADC should be constant.

Woz, thanks for inflator hose tip!

undrh2o

Nice work - I'm working on one now - which cells are you using (K1D, R22)? What gain are you using in the op amp?

Thanks
Chris