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nuno12345
Joined: 16 Jul 2008
Posts: 50
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| 16F88 input(), LDR and ultrasonic |
 Posted: Fri Aug 08, 2008 7:54 pm |
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input():
I'm trying to use input(..) command, thing is..I can use it, but when the pin I'm trying to read is disconnected, it reads random values. I think this is affecting my ADC too, I try to use read_adc() but it always read like 2.20V or so when the pin is disconnected, I can only get a fixed value when I use a POT on it. But when I try to use an audio source for example it always have that 2.20V messing with it.
In input() if I connect PIN_B0/we to GND it reads 0, VDD=1, but when the pin is disconnected it should read 0, and it reads like 01001110/we :P
| Code: | #include <16F88.h>
#device adc=10
#fuses INTRC_IO, NOWDT, NOPUT, NOBROWNOUT, NOMCLR, NOLVP, NOPROTECT
#use delay(clock=4000000)
#include "flex_lcd.c"
void main()
{
setup_adc( ADC_CLOCK_INTERNAL );
setup_adc_ports(sAN0);
set_adc_channel( 0 ); // AN0
lcd_init();
while(1)
{
printf(lcd_putc, "\fINPUT: %i", input(PIN_B0));
delay_ms(100);
}
} |
ldr:
In a normal ADC I can read, well, at least notice differences with audio sources POTs etc, but I can't notice any difference with a LDR, does anyone know why? :/
I tried to use a transistor (BC548) but nothing, my ADC always shows the same voltage, there's no difference :/
ultrasonic:
I got from an old robot 2 pairs of ultrasonic receivers and transmitters, thing is, I know which are transmitter and receiver, VCC and GND pins, but I don't know which frequency they work with (37khz?, 40khz?), how can I "know" it, they don't have any kind of reference ?
Also, I use Proteus to check the frequency I'm producing, its not always 37000, or 40000 it doesn't have to be like that right ? It can be 37100 or whatever right ?
Also, anyone that has experience with ultrasonic "things" in the receiver I only have to use read_adc() make some calculations and I have the distance right ?
Does the transmitter have to be connected to an amplifier or something ?
Well thats all for now :P
Thank you all ;) |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Aug 09, 2008 4:48 pm |
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| Quote: | | I can use it, but when the pin I'm trying to read is disconnected, it reads random values. |
That's completely normal. If you want to hold an unused input pin at
some logic level (high or low), then you must put a pull-up or a pull-down
resistor on the pin. Try it. For the 16F88, you can turn on the Port B
pull-ups with this CCS function:
| Code: | | port_b_pullups(TRUE); |
Put that line of code near the start of main(). Then run your program.
Pin B0 should now read as a logic "1" level.
If you have questions about your LDR and ultrasonic devices, then post
the manufacturer and part number of each device. |
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nuno12345
Joined: 16 Jul 2008
Posts: 50
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| Posted: Sat Aug 09, 2008 5:26 pm |
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Thanks...
Well, can that pullup thing be configured only for some pins? Im using a LCD (PORTB)+ADC(PORTA) will that be affected if I use the pullup? (Sorry for asking instead of testing, but I cant test it right now).
As for the LDR/ultrasonic...They are not indetified with nothing, no number, no reference :/
EDIT:
Tested, theres no interference with the LCD, but why cant I use port_a_pullups? |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sat Aug 09, 2008 6:46 pm |
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Download and read the data sheet for the 16F88.
http://ww1.microchip.com/downloads/en/DeviceDoc/30487c.pdf
Look in the section on I/O Ports. If the PIC has the option to
enable/disable internal pull-ups on a port, it will tell you in that section.
Read the sections on Port A and on Port B. |
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nuno12345
Joined: 16 Jul 2008
Posts: 50
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| Posted: Sat Aug 09, 2008 7:46 pm |
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| Ok, checked, only PORTB has pull-ups :/ this means I cant get a fixed ADC :/ ill try some other ways.. |
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Guest
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| Posted: Sat Aug 09, 2008 7:54 pm |
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| PORTB has _internal_ pullup resistors, PORTA does not. That doesnt mean you can't put your own pull up resistors on PORTA. |
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nuno12345
Joined: 16 Jul 2008
Posts: 50
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| Posted: Sat Aug 09, 2008 9:05 pm |
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Well I do it but it keeps the same :/.
Can you show me a schematic on how to connect a resistor so I can have a stable ADC?
Thanks |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Sun Aug 10, 2008 12:13 pm |
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Here is a schematic of a 47K pull-down resistor on pin AN0:
| Code: |
|-------|
| PIC |
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ADC >--------|AN0 |
signal | | |
| | |
| |-------|
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---/\/\/\/---|
47K |
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-----
---
- |
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nuno12345
Joined: 16 Jul 2008
Posts: 50
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| Posted: Sun Aug 10, 2008 12:34 pm |
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Thanks, I was connecting a 470k resistor :/ lol
It worked, thank you all ;) |
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