Design and building an inexpensive Heads UP or Down Display

York

As Stephane had mentioned earlier, it might be prudent to go for a higher ratio when dividing your battery voltage - replace R19 with at least 200K, better 300 K. You don't loose much in terms of precision, but it will allow you to increase battery voltage should you want a different battery. 300K will allow you to attach up to 20V, which is the rating of your 78L05. With R19=100K your max. allowed battery voltage is 10V before it will affect your PICAXE - too close to your 9V battery voltage.

It's odd that yo get NO backlight at all with 50 Ohms - sure you didn't accidentally use 50K? (Sorry, grasping here ...) Can you measure the current you get with a small resistor?
Reading the data-sheet of your display, your backlight-voltage should not exceed 4.6 Volts, which would allow for a maximum current consumption of 160 mA. If you attach 5 Volts, your current consumption is going to be much higher - you will need some kind of either current-limitation (resistor) or voltage-limitation (adjusteable v-reg). You're lucky you didn't end up with pop-corn...

I can't see what you are doing, so please forgive me if I'm asking rather basic questions. How are you currently running your circuit? On a prototyping-board with push-in connections? Those are notoriously bad for higher currents in combination with precision-voltage. What can happen if you attach your backlight-Ground to GND on the board is that you end up "lifting" the GND-level by a quite a few mVs (because of a bad GND-connection somewhere that acts as a resistor - gets worse over time as contacts corrode), which might also explain the sudden shift in voltage. Make sure your backlight-Ground is attached as close to the battery as possible, best even soldered directly to the battery-connector. Don't assume that connection=connection, even on professionally etched boards some traces need to be extra-big for higher currents (although 160mA are not that big).

I had not followed this thread from the beginning, but looking through your code, am I correct in that you take the two switched to initiate calibration (with the two switches need to be pushed)? why don't you simply put SW1 and SW2 in series instead of blocking two input-pins?

Make sure you publish plenty of pics once you get that thing into the water.

Last but not least, a disclaimer is in order here: don't listen to my ramblings, I'm not an electrical engineer or technician (I am currently best described as microbiologist), it all comes with the best of intentions though ...

Joerg

Corallaro

Hi Joerg

i think to have more precision to be close to my battery voltage but
effectively if i will change battery type......

when i test backlight i use a diode in series to drop 0,7 volt so 5-0.7 =
4,30....and tests have beeen quik...and first i test with a 100 ohm then
with two 100 ohm in parallel, and i measure the resistance, I have had your
same doubt...

i'm using a multihole board with a tridimensional cablage
where i am i don't have my photocamera but only a cellular so i dont' make good photos

i send an old photo with only picaxe into

about the buttons i make the hardware to think to various use/evolutions so i mount this two buttons that in this mode i can use either o singularly

Giovanni

PS
I am an employee in one legal study

Attached Images

Next3.jpg (89.2 KB, 400 views)

York

so you are soldering the board? that should eliminate that idea ...

When you use the extra resistor (100 Ohms) for your backlight you woun't need the diode. Still odd.
Here are a number of adjusteable voltage regulators for your backlight in case you want to do this instead of an in-line resistor. All fairly cheap:

These are rated for 100mA in the same housing you use now.
LM317L from National Semiconductor
TL317 from Texas Instruments

These have a higher rating:
LM317MT from STMicroelectronics
LD1085Vor LD1086V from STMicroelectronics, you will need the suffixes 15-36, not higher (i.e. LD1086V33)

There are many more out there, the trouble is to find them. See which one you can get at your supplier. You can find the data sheets at Electronic Component Datasheets and Data Books The data sheets will also give an example on how to hook them up. By now you probably have realised how much work goes into just reading data sheets and looking for the right components.

good luck getting all the kinks out
Joerg

Corallaro

Hi Joerg

I replace R19 with one of 330kohm and now from test with my batteries:
;battery=ADC
; V 9,17 = 097
; V 8,46 = 088
; V 8,13 = 085
so:
symbol lowbat = 80 ; ADC value for minumum level of battery 80
to optimize with a variable power supply to take the value of ADC at 7,5 - + 8 volt

and then i study better the backlight problem....

I also wait from china a Blue LCD so make a comparison

Giovanni

Stephane

Now that my tools are packed for my trip, I have time to play!

I've just made some measurements on the backlight of a HammerHead display (controler is dead but the LCD display is OK).
It's a Powertip PC1602Q and I think it is very similar to the one Giovanni has.

It starts to emit light at around 3,7V
3,9V : 60mA
4,0V : 100mA
4,1V : 138mA
4,2V : 180mA

For me, 60mA gives a light that I think is enough to see the characters.

Look at this datasheet, there is an exemple of how to use a 78XX regulator as a current source (page 7).

__________________
Stéphane

Corallaro

Hi Stephane

for the moment i prefer debug/optimize your right idea to use the adc free in order to verify the battery

the low battery was a problem that i had left in standby....

instead now it is on the way to solve it

an then....i see on the web if i found solutions/examples about backlight problem, my LCD seems to want maximum power or nothingh light!!
now i remember that i make another test..i have used two diodes in series 5-0.7-0.7=3,6 volt but backlight invisible!!!..


Giovanni

Corallaro

Hi Guys
some closeup of my circuit...no news about soft e/o hardware .....
I'm too much engaged with an HARD TEST with my IDA-71!!!
Giovanni

PS
(lesson learned: don't dive under 15metres with a buddy with o.c. even if your buddy is your reb Guru)

(II lesson learned: even if you broken your drysuit, when you think to have a dive around 33 metres with a buddy in O.C. don't use your old little fins even if they are the only that you can use without drysuit shoes) ....

(III lesson learned: if you don't learn the previous lesson...use IDA-71 only with two scrubbers, this can save you!!)

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Corallaro

Hy Guys

the new release of soft...
i decide to have new graphic... in the tentative to make it more readable...

i use a 16 x 2 dispaly
the first line contain the reading of ADC so, the value in PPO2 of the two cells and a much much approximate value of level battery
in this format "C","1","1.30","C","2","1.30","#","9".
C,1,2,# are redefined inverted/negative chars to make it more readable

the second line is only used for messages
"oxygen setpoint" (when all is OK)
"* BATTERY LOW *"
"* CELL WARNING *"
"* LOW OXYGEN *" (too low or
"* HIGH OXYGEN *" too high oxy)
"- low oxygen -"
"- high oxygen -"

at the moment the code isn't debugged and isn't optimized...and now with the redefined char isn't possible the complete emulation

a problem to solve...

current for the leds

the base circuit need 5+-7 milliamperes to work but when the led/s on it arrive until 20-22 milliamperes so, i think to increase the limitation resistor of the led..(a unique new resistor from negative of leds to ground) until to have the minimum luminosity..
but, exists some leds more efficient ( + luminosity - current)??

Giovanni

Attached Files

V0.62B_DIRECTLCD_ALARMCELL_TESTBAT_CHARMOD.zip (3.3 KB, 31 views)

Corallaro

Hi Guys
today, from china, is arrived a "reverse"/"negative" BLUE LCD so i make some test
this lcd is readable only with backlight
i see that it give more light and need minus current instead my normal green LCD
so i make some test/mods and add:
R21= 100 ohm to limit current of LCD backligh to +-15 ma (to have a minimum sufficient light to see it darkness)
sw3=reed switch for backlight
in this mode the current in milliamperes

with blue LCD
5,6 led off
6,9 led on
17,8 led and backligh on (much luminous)

with green LCD
5,8 led off
7,0 led on
20,0 led and backlight on (little luminous)

so i add also

R20= 330 ohm to limit current of led (to save battery) but is more resonable a value of 270 ohm (the light is a little low)

in this mode the current in milliamperes

with green LCD
5,8 led off
6,6 led on
19,6 led and backlight on (little luminous)

to test it i connect the milliamperometer to positive of 9vcc battery and this values aren't fix...so the little imprecision

Giovanni

Attached Images

Immagine 1.jpg (228.0 KB, 324 views)

Corallaro

Hy Guys.....

do you abandoned me???? sighhhh!!!!!!!!!!!

so, i think to be at the end of big variations upgrade....

in this version i add a setpoint routine
now there are three modes:
HIGH SP (default)
LOW SP
MANUAL (hud disabled, only battery-alarm and cell-alarm)

When i start for the first time the cicuit, the setpoint is high, but all reading is zero, you must calibrate in pure o2.

So push either buttons (first pin6 and then pin7 and take its pushed) to enter in calibration menu
the limits are betwen values 80-120 (i think to use 90-110)
release one of pin to exit from calibration routine, if value is ok the circuit is calibrated.

Now the circuit works with high setpoint and:
for value of ppO2 from 1.25 to 1.40 only green led on and write on LCD "oxygen setpoint"
for value of ppO2 from 0,50 to 1,25 green led on and yellow led blinking (slowly) and write on LCD "- low oxygen -"
for value of ppO2 from 0 to 0,50 green led off and yellow led blinking (fast) and write on LCD "* LOW OXYGEN *"
for value of ppO2 from 1.40 to 1,55 green led on and red led blinking (slowly) and write on LCD "- high oxygen -"
or value of ppO2 from 1,55 to high, green led off and red led blinking (fast) and write on LCD "* HIGH OXYGEN *"

if i want change setpoint i can push only one button (pin7)
when i push it the circuit freeze until i release it.
when i release i see that the fist simbol of first line of display is changed, from reverse H to reverse L.
now i am in "low setpoint" and:
for value of ppO2 from 1.25 to 1.40 only green led on and write on LCD "oxygen setpoint"
for value of ppO2 from 0,50 to 0,60 green led on and yellow led blinking (slowly) and write on LCD "- low oxygen -"
for value of ppO2 from 0 to 0,50 green led off and yellow led blinking (fast) and write on LCD "* LOW OXYGEN *"
for value of ppO2 from 0.80 to 1,55 green led on and red led blinking (slowly) and write on LCD "- high oxygen -"
or value of ppO2 from 1,55 to high, green led off and red led blinking (fast) and write on LCD "* HIGH OXYGEN *"

now if i push the button (pin7) and release it i see that the first simbol of first line of display is changed, from reverse L to reverse M and on bottom of LCD there is wrote "- HUD disabled -"
in this mode the HUd is off and only battery-alarm and cell-alarm works, the value of cells are obviously readable...

If i off circuit when then on it, the value of last calibration are stored in memory, the value of setopoint NO, i think to have of default high setpoint .....

what do you think??????????????????????????????????

Giovanni

PS
the code isn't optimized and isn't debugged well

Attached Images

CIRCUIT.jpg (36.1 KB, 269 views)

Attached Files

V0.64B_SP.zip (3.6 KB, 27 views)