Very Small Panel Meters

Stephane · 5th November 2007, 14:04

Quote: (Originally Posted by teomannaskali)

I have no problem in soldering smd's. I soldered about 2200 of them the other day.

Can I send you my PCB ?

The problem is not to solder a component but to know which one has has to be modified.

teomannaskali · 5th November 2007, 14:15

THat is the easy part. They tell you which one you have to modify in the data sheet in the previous post that I sent. If you put the reference voltage that they provide down then it will measure lower voltages.

One veeery important question however. Did you dismantle the Display. Can I remove the PCB at the bottom and then replace it without damaging the display? It seems to be just held in place by little tabs at the side.

If so then It will be perfect!

Teoman

Stephane · 5th November 2007, 14:25

I will post a photo tonight as I don't have the download cable with me.
Opening the SP400 is easy.

teomannaskali · 5th November 2007, 14:44

Yep indeed opening it is a piece of cake

It is the closing it part that I am worried about.

Ok it all seems doable for now... I will have to check the dataseet for the specifications of the device...

Does anyone have any good reason to believe that converting this pm will not work? So I do not waste my time and my money (I paid 28 dolars for one of these dpm's)

Teoman

teomannaskali · 5th November 2007, 15:03

For those you who will try to follow here is a link that explains how the DPM's work

http://hallaweb.jlab.org/tech/jackja..._app_notes.pdf

Teoman

bigbutsilent · 5th November 2007, 16:41

Hi all,

Why do you want to destroy a lascar display - you dont need to. If you can wait till Tues I will send you a layout that works. I make these on a commercial level - trust me trying to solder smds is a pain.
Datel do a realy cheap display - but the backlight and stability are better with the lascar.

teomannaskali · 5th November 2007, 17:20

I have no problems soldering smd's

Does your solution involve an op am? Or modifying the display to sue the op amp provided?

I am very interested

At the moment if I am not mistaken. If I change the Ref voltage to the display from 100mV to 49 mV (by changing the value of one resistor from 100k to 200k) THen I can connect my cell directly to the display without any other equipment

Not forgetting the 10K load of course.

Tell me this is not so simple before it gets expensive please.

Teoman

Stephane · 5th November 2007, 17:39

Teoman,

I can try to make the modification on my "dead" DPM (some LCD bars are dead so I can't read correctly the value) if you want, just tell me what component I must change.

teomannaskali · 5th November 2007, 18:26

I will get back yo you tomorrow. When I have verified that it will work.

What I have in mind is: if you look at the circuit diagram in the link:
http://www.lascarelectronics.com/data/pdf/SP%20400.pdf

By default the display is a VOLTMETER with a gain of 10.
This means that if there is a difference of 199.9mV between in_Hi and IN_Lo then it will show 1999. (After this you add the "." wherever you want)

So. We have 10mV that we want to show as 209 that is a gain of 20.9.
http://hallaweb.jlab.org/tech/jackja..._app_notes.pdf

From this site we get:
READING = 1000 * VIN / VREF

(Originally Vref is set to be 100mV and with the small calibration pot under the display you change this to 100mV if it is not exactly that)

And the circuit that creates this vref is:

V_PLUS--------(100K)------+----(3K)-----(1K POT)-----Vref_LO

VRef_HI is connected to where that + is.

PS:The editor deletes all white spaces so it is difficult to do ascii drawings.

So we want to set to half its value.
We will exclude the pot for now.

VRef_HI = 3/103 * V_PLUS

To get 1/2Vref we would Need to change the 100K resistor to a 203K resistor.

That resistor is R4, now I did not dare to remove the backlight from the display. But if you have an ohmmeter then you should be able to tell which one it is. The circuit diagram does not show any other 100K's. Just one other 130K for the battery indicator light. If you follow from the pot then first you will find a 3K then a 100K resistor.

Where did you get the lascar from? And how is it used in its original configuration? How did it die? I know they do not like pressure or water.

Teoman

teomannaskali · 5th November 2007, 18:29

Have you tried cleaning the contacts where the LCD part connects to the pcb part?

Or have just the LCD part in you hand and randomly touch the bottom of it. The electricity in you hands is quite enough to keep some segments of the lcd lit for some time. See if the dead segments are really dead or there is just a connection problem.

5th November 2007, 14:04	#11 (permalink)
Stephane Hey! Ho! Let's go! Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Nantes - France Posts: 742	Re: Very Small Panel Meters Quote: (Originally Posted by teomannaskali) I have no problem in soldering smd's. I soldered about 2200 of them the other day. Can I send you my PCB ? The problem is not to solder a component but to know which one has has to be modified. __________________ Stéphane Hammer-rEvo powered!
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5th November 2007, 14:15	#12 (permalink)
teomannaskali Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Feb 2006 Location: Istanbul TR Posts: 350	Re: Very Small Panel Meters THat is the easy part. They tell you which one you have to modify in the data sheet in the previous post that I sent. If you put the reference voltage that they provide down then it will measure lower voltages. One veeery important question however. Did you dismantle the Display. Can I remove the PCB at the bottom and then replace it without damaging the display? It seems to be just held in place by little tabs at the side. If so then It will be perfect! Teoman Last edited by teomannaskali : 5th November 2007 at 14:23.
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5th November 2007, 14:25	#13 (permalink)
Stephane Hey! Ho! Let's go! Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Nantes - France Posts: 742	Re: Very Small Panel Meters I will post a photo tonight as I don't have the download cable with me. Opening the SP400 is easy. __________________ Stéphane Hammer-rEvo powered!
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5th November 2007, 14:44	#14 (permalink)
teomannaskali Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Feb 2006 Location: Istanbul TR Posts: 350	Re: Very Small Panel Meters Yep indeed opening it is a piece of cake It is the closing it part that I am worried about. Ok it all seems doable for now... I will have to check the dataseet for the specifications of the device... Does anyone have any good reason to believe that converting this pm will not work? So I do not waste my time and my money (I paid 28 dolars for one of these dpm's) Teoman
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5th November 2007, 15:03	#15 (permalink)
teomannaskali Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Feb 2006 Location: Istanbul TR Posts: 350	Re: Very Small Panel Meters For those you who will try to follow here is a link that explains how the DPM's work http://hallaweb.jlab.org/tech/jackja..._app_notes.pdf Teoman
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5th November 2007, 16:41	#16 (permalink)
bigbutsilent New Member Current Rebreather/s: Other SCR Home Build Other Rebreather/s: Not Bought Yet MK 15.X Other SCR Home Build Join Date: Feb 2007 Location: Central England Posts: 2	Re: Very Small Panel Meters Hi all, Why do you want to destroy a lascar display - you dont need to. If you can wait till Tues I will send you a layout that works. I make these on a commercial level - trust me trying to solder smds is a pain. Datel do a realy cheap display - but the backlight and stability are better with the lascar.
(Offline)

5th November 2007, 17:20	#17 (permalink)
teomannaskali Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Feb 2006 Location: Istanbul TR Posts: 350	Re: Very Small Panel Meters I have no problems soldering smd's Does your solution involve an op am? Or modifying the display to sue the op amp provided? I am very interested At the moment if I am not mistaken. If I change the Ref voltage to the display from 100mV to 49 mV (by changing the value of one resistor from 100k to 200k) THen I can connect my cell directly to the display without any other equipment Not forgetting the 10K load of course. Tell me this is not so simple before it gets expensive please. Teoman
(Offline)

5th November 2007, 17:39	#18 (permalink)
Stephane Hey! Ho! Let's go! Current Rebreather/s: rEvo Other Rebreather/s: rEvo Join Date: Nov 2005 Location: Nantes - France Posts: 742	Re: Very Small Panel Meters Teoman, I can try to make the modification on my "dead" DPM (some LCD bars are dead so I can't read correctly the value) if you want, just tell me what component I must change. __________________ Stéphane Hammer-rEvo powered!
(Offline)

5th November 2007, 18:26	#19 (permalink)
teomannaskali Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Feb 2006 Location: Istanbul TR Posts: 350	Re: Very Small Panel Meters I will get back yo you tomorrow. When I have verified that it will work. What I have in mind is: if you look at the circuit diagram in the link: http://www.lascarelectronics.com/data/pdf/SP%20400.pdf By default the display is a VOLTMETER with a gain of 10. This means that if there is a difference of 199.9mV between in_Hi and IN_Lo then it will show 1999. (After this you add the "." wherever you want) So. We have 10mV that we want to show as 209 that is a gain of 20.9. http://hallaweb.jlab.org/tech/jackja..._app_notes.pdf From this site we get: READING = 1000 * VIN / VREF (Originally Vref is set to be 100mV and with the small calibration pot under the display you change this to 100mV if it is not exactly that) And the circuit that creates this vref is: V_PLUS--------(100K)------+----(3K)-----(1K POT)-----Vref_LO VRef_HI is connected to where that + is. PS:The editor deletes all white spaces so it is difficult to do ascii drawings. So we want to set to half its value. We will exclude the pot for now. VRef_HI = 3/103 * V_PLUS To get 1/2Vref we would Need to change the 100K resistor to a 203K resistor. That resistor is R4, now I did not dare to remove the backlight from the display. But if you have an ohmmeter then you should be able to tell which one it is. The circuit diagram does not show any other 100K's. Just one other 130K for the battery indicator light. If you follow from the pot then first you will find a 3K then a 100K resistor. Where did you get the lascar from? And how is it used in its original configuration? How did it die? I know they do not like pressure or water. Teoman Last edited by teomannaskali : 5th November 2007 at 18:33.
(Offline)

5th November 2007, 18:29	#20 (permalink)
teomannaskali Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Not Bought Yet Home Build Join Date: Feb 2006 Location: Istanbul TR Posts: 350	Re: Very Small Panel Meters Have you tried cleaning the contacts where the LCD part connects to the pcb part? Or have just the LCD part in you hand and randomly touch the bottom of it. The electricity in you hands is quite enough to keep some segments of the lcd lit for some time. See if the dead segments are really dead or there is just a connection problem.
(Offline)

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