flowcode pic16F88 and output

mohandino · Post by **mohandino** » Thu Jul 12, 2007 8:07 pm

Hi,

I whant to know if the 16F88 chip has en analog outpout and how can i use it with flowcode ( v2 i prefer

)

thanks

hmcleod · Post by **hmcleod** » Fri Jul 13, 2007 12:08 am

I've not used many different PICs, but I don't think any of them have analogue out

Post by **Benj** » Fri Jul 13, 2007 9:25 am

You can create an analogue output by using a PWM output connected to a capacitor. It will take some tweaking to get the PWM frequency to match the capacitor charge rate. Then you should be able to set a mark space on the PWM and get a linear analogue voltage out.

Code: Select all

PWM O/P ------ Cap + --------- Analogue out
               Cap -
                 |
               GND

Post by **Steve** » Fri Jul 13, 2007 9:41 am

The voltage will vary depending on the load, so you may additionally need an opamp (for example).

Alternatively, use a DAC.

mohandino · Post by **mohandino** » Fri Jul 13, 2007 10:30 am

Benj wrote:You can create an analogue output by using a PWM output connected to a capacitor. It will take some tweaking to get the PWM frequency to match the capacitor charge rate. Then you should be able to set a mark space on the PWM and get a linear analogue voltage out.
Code: Select all
PWM O/P ------ Cap + --------- Analogue out
               Cap -
                 |
               GND

Hi thanks for your help, the current needed is 2mA. How can i initialised the pwm in flowcode v2 ?

Post by **Benj** » Fri Jul 13, 2007 10:33 am

Hello

In flowcode 2 you will need to create your own C or assembler functions to control the PWM.

Flowcode V3 comes with a PWM component that makes this task a lot easier.

mohandino · Post by **mohandino** » Fri Jul 13, 2007 10:53 am

Benj wrote:Hello

In flowcode 2 you will need to create your own C or assembler functions to control the PWM.

Flowcode V3 comes with a PWM component that makes this task a lot easier.

OK but if you can copy the code genereted by flowcode v3 for the PWM component, i'll be happy

thanks

ps : is there a solution with Add Defines pwm ?

Post by **Steve** » Fri Jul 13, 2007 2:49 pm

The code generated by Flowcode V3's PWM component is very bloated for your needs. Also, it is designed for a different compiler than C2C and so it will not work without modification.

I suggest you look at the datasheet for the PICmicro you want to use instead. The section on PWM generation is pretty good and should explain everything you require. For example:

15.4.4 SETUP FOR PWM OPERATION
The following steps should be taken when configuring
the CCP module for PWM operation:

1. Set the PWM period by writing to the PR2 register.
2. Set the PWM duty cycle by writing to the CCPRxL register and CCPxCON<5:4> bits.
3. Make the CCPx pin an output by clearing the appropriate TRIS bit.
4. Set the TMR2 prescale value, then enable Timer2 by writing to T2CON.
5. Configure the CCPx module for PWM operation.

mohandino · Post by **mohandino** » Fri Jul 13, 2007 9:08 pm

hi

i found the solution see this site in french

http://isi-si.chez-alice.fr/flowcode/flowcode.htm

I've a new problem. I whant to change the light of a seven digit display by using the pwm. Is someone knows the frequence to have a output 1V< CCP1< 5V ?

thanks

Post by **Benj** » Mon Jul 16, 2007 9:16 am

Thanks for the link.

You need a PWM frequency that is fast enough to acheive a good refresh rate. Then you can simply change to mark space ratio to control the brightness of the display.