HELP me build a gas gauge????

[chemelec]

Jut to Update Everyone, "browningbuck" advised me in an email he would now like 6 LED's.

One of these to go elsewhere on the display.

Here is the schematic that I sent him. Its Tested and works in bar mode or dot mode.

He can either use an LED on Pin 1 or put 2 Leds on Pin 18, for what he was asking to do.

But now it seems has isn't familiar with a Potentometer symbol. I just emailed him a reply on this.

Hope this all helps him.

Merry Christmas to all......Gary.

 

[on1aag]

Hi Browningbuck,

I made a slight error in my previous design, I thought that the
resistance of the gas gauge increased with the level of fuel in
the tank but unfortunately it was the other way about.
So I built a new one and added the sixt led.
No regulated power supply needed, fewer parts, simpler, cheaper.

on1aag.

 

[browningbuck]

HELLLLLLOOOOOO AGAIN

well this thing works....but i need a little help...

so here is how its wired up now

**broken link removed**


i need to know if there is a way to have pin 1 of the LM3914 only light the led up once that pin 18 no longer has power.....

so the idea is once the pin 18 led dies out the pin 1 will kick on...not stay on at ALL times.

any help???? thanks in advance guys you have really helped me out on this project(the easiest fix is the most preffered )

and how would a i wire up a photoresitor into this so that the leds would dim as it gets darker (the pin 1 led does not need the dimming function...only pins 10-18)????

Brian Harris
Motydesign.com

**broken link removed**

 

[browningbuck]

bump for some help please

just need to figure out how to get pin 1 to light up once pin 18 is no longer powered

 

[Hero999]

Why do you want to do that?

You could just connect an inverter to the pin 18.

 

[browningbuck]

the reason i want this is so that when you are riding 5 leds that re in bar mode (18 17 16 15 14 ) show full to empty....but once empty light goes out pin 1 lights up under a gas symbol giving you the signal you are on reserve...how does the inverter work???

 

[Hero999]

The LED comes one when pin 18 goes high and turns off when it goes low.

All you need to do is connect a logic inverter (not gate) to invert the signal.

You could use the other half of the op-amp with a couple of resistors to shift the voltages as an inverter.

 

[browningbuck]

well its a good thing i have another opamp avilable...it sucks i cant use the onle thats already on there

HERO you are my hero...ahahha thanks i will wire it up tomorrow and post it up.

 

[kchriste]

The LM358 is a DUAL opamp. Hero999 has shown you how to use the other one in the chip.

 

[browningbuck]

ahhhhhhh i get it now i didnt notice the pin #s SWEETTTT... i get pics up tonight

thanks for the clairification that i over looked....

i did have anothe question though waht is with the 220 resistor coming off pin 18? is there more voltage going out of the opamp that would cause the led to be brighter than the others if it wasnt there...and if that is not the case will the led be dimmer than the others...if this doesnt get answered by tonight i gues i will know from looking at it lit up.



once again guys thanks this thing has just bl;own up in complexity compared to my original idea
Brian

 

[kchriste]

The LED connected to pin18 will be just as bright as before. The 220hm: resistor is there to give an extra voltage swing for the opamp so it can detect the "empty state" better. The brightness of the "Gas Empty Light" is set by the 820hm: resistor.

 

[Hero999]

That's right, in order for the op-amp to be able to see the voltage difference between the inverting and non-inverting input, the voltage on both pins needs to be <Vcc-2 and this is what the additional resistors do.

 

[browningbuck]

well it worked.... needed some resistance tweaking here and there but the pots helped me figure out exactly what i needed.... HERO thanks again for the quick response to a easy yet very efective fix using compnents on the board... i will get the vid up tonight...and pics of the final work fully installed this weekend


Brain

 

[browningbuck]

as promised here is the working board

**broken link removed**

 

[Hero999]

Good you got it working.

How are you planning to assemble this, are you going to use a PCB or veroboard?

 

[browningbuck]

unforutantly i will be using Veroboard for the first two i build....i will be doing my Gebers this week, and get them sent off to china to get my first 100 unit batch in the next few weeks

 

[seuadr]

Jut to Update Everyone, "browningbuck" advised me in an email he would now like 6 LED's.

One of these to go elsewhere on the display.

Here is the schematic that I sent him. Its Tested and works in bar mode or dot mode.

He can either use an LED on Pin 1 or put 2 Leds on Pin 18, for what he was asking to do.

But now it seems has isn't familiar with a Potentometer symbol. I just emailed him a reply on this.

Hope this all helps him.

Merry Christmas to all......Gary.

i've just found this thread by searching for the same thing browningbuck was, and the schematic looks great, i've located a local parts store and got both LM358
and
LM3914

the gentleman helping me there thought to help me pick out the correct resistors, when i realized.. i don't know what wattage these resistors are supposed to be? i'm really new to all of this, so i may just be missing something that is obviously right infront of my face. I appoligize if that is so.

 

[kchriste]

With the exception of the 380hm: resistor (connected to sender) and the 330hm: (connected to the 2.5V zener), both of which should be 1/2watt or better, the rest can be 1/4watt resistors.

 

[seuadr]

fantastic!

fantastic!

i got the controler and the amp today, tommorow i make a foray to radio shack to get the rest of the components.. and possibly a bar of LED bulbs containing 10, if i can find one. i don't have a seperate area for the emergency fuel light, but i saw a bar online today with 9 greens and a red, seems to me the red would work fine in that situation.

Today, after visiting the local radio shack, i was lucky in that one of the employees is apperantly a retired electrical engineer, so he's gonna make sure i don't get the wrong resistors, because, frankly, the coloured bands are to show you what the stats of the resistor is.. and that is ALL i know about them

fantastic work here.. made things easy even for a total noobie such as myself! i appreciate it greatly.. similar units, while being billet or nice chrome or whatever do the same thing, and sell for 250-500 dollars.. being able to do this for what looks like a total of about 20 dollars and just my time invested is a huge coup for my wallet! thanks again

 

[Hero999]

It's easy to adapt this for 10 LEDs as the IC was origionally designed for 10.

browningbuck,
So I take it you're now planning on selling this. If you ever return, please post a picture of the finished PCB.