Re: [Paparazzi-devel] Blank GCS frame!

[Michel GORRAZ]

Hello guys,

Please, don't change the resistors : it's useless
because you can easily compute the "coefficient" used in "tiny_2_1.h" and
it's dangerous
because if you use a wrong value, you can DESTROY the ADC input !!!

In " #define VoltageOfAdc(adc) ( coeff *adc) " let :

• adc = raw value of the ADC input measuring battery voltage. LPC2148 are 10bits ADCs, so the raw value in software always between 0 and 2^10 (=1023)
• Vref = LPC2148 ADCs ref voltage = LPC2148 main power supply = 3.3v
• R1, R2 = resistors made up the bridge of the battery voltage measurement system (see schematic)
• R1 between Vbattery & ADC input
• R2 between ADC input & ground

The general formula to compute the  coefficient is :

coeff = ( Vref  / ( 2^10 - 1 ) ) x (1 + R1/R2)

coeff = ( 3.3 / ( 1024 - 1 ) ) x (1 + R1/R2)

coeff = 0,0032258 x (1 + R1/R2)

For example :

Tiny 1.1 : R7 = 15k, R15 = 3.3k => coeff = 0,0178885630
Tiny 2.1 : R1 = 15k, R2 = 3.3k => coeff = 0,0178885630
Tiny 2.11 : R1 = 10k, R2 = 1.5k => coeff = 0,0247311828

But, it's an approximate value because of the dispersions of the components :

• resistors values (+/-1% or 5%)
• power supply (not exactly 3.3v)
• etc.

So, calculate your own board "coeff" according these two resistors values and if necessary adjust it with the GCS voltage indication and several battery voltage values (use a power supply)

@+
Michel

PS : note that R1 & R2 values where modified between Tiny 2.1 and 2.11 to minimize the amount of resistors values, so the cost...

2008/5/1 Michel GORRAZ <address@hidden>:

Hello guys,

Please, don't change the resistors : it's useless because you can easily compute the "coefficient" and it's dangerous because if you use a wrong value, you can DESTROY the ADC input !!!

Let :

2008/5/1 Simon Jobin <address@hidden>:

hi,

For your voltage problem, as Anton said this is because your resistor bridge is wrong. Here are some ways to solve to problem

1) had  to your airframe conf file. This will generate warnings because VoltageOfAdc(adc) is already defined in tiny_2_1.h. The #ifndef i tiny_2_1.h doesn't help since this file is probably built before.

2)change your resistors bridge for values that respect the ratio in tiny_2_1.h

Simon
________________________________
> From: address@hidden
> Date: Wed, 30 Apr 2008 20:28:28 +0000

> To: address@hidden

> Subject: RE: RE: [Paparazzi-devel] Blank GCS frame!

>
>
> Yes, u-center defaults to temporary settings, you must check the box to make it permanent and you may need to upload the settings twice if the baud rate change causes the upload to fail.  Power cycle it to be sure it holds the new settings.
>
> The tunnel code allows u-center to see the gps, this is the only purpose of the tunnel - to bypass the autopilot and communicate directly with the gps.  When you flash with regular code, only the autopilot can communicate with the gps and it will send pprz data down the serial port that only the pprz GCS can interpret.
>
> -- address@hidden wrote:
>
> When you use Ucenter, you must click a box to save to flash memory.  I dont quite remember where, but I think its on the wiki.
>
> AJ
>
> -------- Original Message --------
> Subject: Re: RE: [Paparazzi-devel] Blank GCS frame!
> From: Mohammad Ali Haji Pour

> Date: Wed, April 30, 2008 7:59 am
> To: address@hidden
>
> BTW I forgot to mention that after uploading the code into the AP, I cannot get anything from GPS in the u center with the FTDI cable.
>
> Best Regards,
>
> Mohammad
>
>
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