Modifying A/F meter (Electronic gurus, help please)

Post by **jtbo** » 24 Mar 2006 10:56 pm

Here is pic of meter that I do have:
http://www.janiervast.com/gallery/v/alb ... ?g2_page=4

Currently leds lit as follows:
led (lambda) A:F
1 0.98 14.4
2 0.97 14.2
3 0.96 14.1
4 0.95 14.0
5 0.93 13.7
6 0.90 13.2
7 0.87 12.8
8 0.84 12.3
9 0.81 11.9
10 0.77 11.3

I would like to change it so that leds will got lit normally, 14,7 would be led 5, but I only know that I would need to change 3 resistors, I don't know which one and I don't know what value those would need to be.

Is it possible to find out somehow?

I don't have powersource that would give proper voltage so I think I need to do just math, somehow.

Is this totally impossible to solve and it would be easier to do new one?

Post by **Chris_C** » 25 Mar 2006 12:12 am

Could you post another pic or two of the back of the board Jani? I'm intrigued as to what the two small chips are, I reckon one has to be a voltage reg, but not sure. Other than that, it's not going to be easy to get a linear display, but I can at least centre it for you!

Edit: right, ones definately a voltage reg, and by modding that we can centre the display at the fifth LED.

Edit again: Ok, so definately isn't. ho hum...

Post by **jtbo** » 25 Mar 2006 12:31 am

Chris_C wrote:Could you post another pic or two of the back of the board Jani? I'm intrigued as to what the two small chips are, I reckon one has to be a voltage reg, but not sure. Other than that, it's not going to be easy to get a linear display, but I can at least centre it for you!

Edit: right, ones definately a voltage reg, and by modding that we can centre the display at the fifth LED.

Wires as follows:
Top +12V
Center Ground
Bottom Lambda signal in

Post by **Chris_C** » 25 Mar 2006 03:29 am

Right, you to get it centred, you need to change (in reference to picture 3784

Green next to IC - option 1 1k option 2 1K2
Green second top - option 1 120R option 2 150R

Must pick either both option 1's, or both option 2's. This will make the voltage range 0.1 to 0.9 volts, centred about the middle (lambda == 1) at 0.5V

As the narrowband is non linear, it will jump from say 4 leds to 6 quite quickly, but at least as there is a larger swing, this effect will be removed as far as possible.

Hope that helps mate, and thank Andy for working thorugh with me

EDIT: Oh, yeah, forgot to mention, as it's half 2, neither me or Andy take any responsibility for broke stuff... all maths was done in paint and my head!

Post by **Chris_C** » 25 Mar 2006 03:38 am

And just to prove it circuit worked out, followed by some maths

Night all...

Post by **jtbo** » 25 Mar 2006 03:40 am

Hehe, thanks guys from helping on this, must look tomorrow if I get that package picked up, I did order resistors, whole E12 series and also E3 series so I should have almost any value now, I guess.

Again, big thanks

Post by **jtbo** » 25 Mar 2006 06:58 pm

Ok, I made changes and it works beautifully, now I just need to place it so that cars behind and side of me can see it

Maybe not

Thanks again from helping with this

Post by **Chris_C** » 25 Mar 2006 07:07 pm

It actually worked?!? Bonza... I'm getting better at this...

Post by **pettaw** » 25 Mar 2006 07:11 pm

Glad it works

Considering I'm just a luddite and it was 2:30am, glad I could help Chris to bounce ideas around

Post by **jtbo** » 25 Mar 2006 07:27 pm

I do have only one lamda so I did connected my A/F meter to same wire that goes to Megasquirt, some A/F ratio meters need to be modified for this, there is usually 1M or 2M resistor for lambda signal and that need to be taken away so it would not cause voltage reading to get messed up, that is what I have read. But this seem to be working fine without modifying.

I think I should take bit of videos from car sometime, now there is lot of flashing lights too