Need help designing a circuit using a preassure transducer

[davekra]

Could one of you kind fellows help me design a circuit?
It’s not exactly for a plane but it is for my car that I use to haul my planes ;)
I’m trying to make a boost gauge using an mpx4250a pressure transducer and 4 lm3914’s.
I’d ask the guys in the car forum I read but us plane guys are much nicer and more intelligent. ;)
If someone would like to PM me I can give you more details.

Thanks,
davidk

[davekra]

No one wants to respond to respond to my general question? How bout more specific ones?
I’m using three of the 3914’s setup in bar mode. The voltage for this goes from 1.7 to 3.2. Reading from the chips PDF for “adjusting linearity of stacked dividers” would I create a resistor network and put 1.7 volts at the first chips Rlo and 2.2v at Rhi. The second would have 2.2v at Rlo and 2.7 at Rhi and the third would have 2.7 and 3.2?

Looking at the “non-interacting adjustments” diagram would I instead create three of these, one for each chip? How would I connect the Rhi and Rlo of adjoining chips using this method.

I need to be able to adjust the brightness of the entire display. Can this be done for all chips using one adjustment? Or will the brightness have to be separate for each chip?

The total voltage range I’m working with is from .2 to 3.2. From .2 to 1.7 is going through one chip setup in dot mode and 1.7 to 3.2 is going through 3 chips setup in bar mode.

Thanks for any help you can give.
davidk

[willfly]

Don't understand what you are are trying to achieve. If it is reading the pressure transducer value into a micro controller, then buffer the sensor with an instrumentation amplifier and use a high resolution (>12 bits) ADC.

If it is simple quantization of sensor output over wider range, then I think you are right on target with using LM3914. Start with one and then add more to expand the range.

[davekra]

I'm afraid your talking on a much higher level than what I understand.
Heres where I am now http://home.wi.rr.com/dkraemer/drawing10.jpg .

I've gotten it to light up the way I want but was having trouble calculating the values with a resistor divider using 6 resistors. So I just changed the drawing to have 5 separate pots set the hi and lo for each chip. Will the 5 pots work?

The other stumbling block is a brightness control. Will the circuit in the box work to control the brightness? Is there a way to controll the brightness for all chips using one adjustment?

If anyone has a more elegant design or other sugestions please let me know.

Thanks,
davidk

[Acetronics]

;)
Hi, dave

Another solution is to use the U 1096 B circuit from Vishay TFK ... it's an oldie, still available, but able to drive alone all your Leds !!!

Alain

PS: Will you be able to stare at your "christmas tree" AND drive properly your car at the same time ???

RePS: Have a look Here : http://www.jaycar.com.au/productResults.asp?FORM=CAT

[davekra]

I know, it's just a bunch of flashy lights. I just enjoy building it, like I enjoy building an Apogee or Supergee. I just wish I had a more indepth understanding of electronics. I intend to intigrate it into the guage cluster in such a way that it looks like it was installed by the factory. None of this gaudy guage stuck on the dash stuff.

Alain, that's a cool site. Lots of neet little projects, but what were you trying to link to? The link didn't find anything.

Thanks,
davidk

[Acetronics]

Dave,

You just have to have choose "kits and modules" and " automotive " to get to the right section : tons and tons of gadgets for your car hood ...

With a little help from my friends, were singing the Beatles ... LITTLE help !!!

Alain

[davekra]

The circuit is complete except for a brightness control. Is there a way to control the brightness on all chips using one adjustment?
http://home.wi.rr.com/dkraemer/Drawing11.jpg
The resistors R1 - R4 control the brightness. I've replaced them with a 2k resistor and a 100k pot which gives me full brightness with a full turn of the pot.

Please, anyone with an idea on how to do this?

Thanks,
davidk

[Mr.RC-CAM]

Is there a way to control the brightness on all chips using one adjustment?You will probably have to setup all the LM3914's for max brightness and then PWM (pulse width modulate) the +5V current that drives the string of LEDs. An LM555 timer, with transistor buffer, should do the trick. Just look at the app notes to the LM555 and see what is needed for astable PWM use.

Perhaps another way is to replace the pots with FET transistors and then drive the FETs in their linear region with a single pot. I'm not sure this will work though.

RC-CAM