schmitt trigger + adc converter

[musicgal]

hihi, i'm aware that adc converter are applicable to micro processor

however i do not know which adc can be used for xilnx cpld chip..

i was told to use schmitt trigger to convert from analog to digital. bt as my knowlege is quite limited i do not know which is the correct ciruit from the internet to get the desired output.





can anyone help me out in this please?

thanks alot


yours sincerely,
musicgal

 

[philba]

In a manner of speaking the schmitt trigger converts to digital but it's just to either 0V or Vcc. It's used to prevent a slowly changing signal from producing a series of pulses. https://en.wikipedia.org/wiki/Schmitt_trigger

what are you trying to accomplish?

 

[dezmondngo]

is there an IC where it converts analog input into digital output but without the inverter? because I've only got my hands on this hex schmitt trigger inverter 74LS14 where it sets the ADC, however it inverts the output into low if my input is high... any idea? I just need an intermediate converter from Analog to Digital before the input goes into the input port of the PIC16F877A microcontroller... any idea guys?

 

[blueroomelectronics]

You might be able to use the 16F877A internal comparator(s).

 

[ericgibbs]

is there an IC where it converts analog input into digital output but without the inverter? because I've only got my hands on this hex schmitt trigger inverter 74LS14 where it sets the ADC, however it inverts the output into low if my input is high... any idea? I just need an intermediate converter from Analog to Digital before the input goes into the input port of the PIC16F877A microcontroller... any idea guys?

hi,
Use two invertors gates in the 74LS14 connected in series, a double inversion will put your signal the right way up.

 

[dezmondngo]

You might be able to use the 16F877A internal comparator(s).

well I need 4 input A0-A3 if I use the internal ADC, I understand the voltage sampling from a single pin_A0 if I set the threshold voltage, but how about the other 3 inputs? the I'm not sure how to command all four inputs to if the input is 0000 or 1111 in a single variable for the if...else statement...

if porta==0110
{
}

if portb== 0011
{
}

 

[blueroomelectronics]

The A/D in muxed (one at a time) and requires low impedance source and acquisition time. The comparators (there are two) are very fast and can generate an interrupt.

If you need 4 inputs and you can use the 74LS14 connected to RB4-7 and any change can trigger an interrupt.

Are you using a FPGA or 16F877A?

 

[philba]

Why do you not want the signals inverted? You can just reverse the sense in you program. Where you would check for 1, look for 0 and vice-versa.

 

[blueroomelectronics]

Why do you not want the signals inverted? You can just reverse the sense in you program. Where you would check for 1, look for 0 and vice-versa.

I was wondering that myself.

 

[dezmondngo]

well I understand it now, thanks a lot.. I'm using PIC16F877A.. because I'm actually doing a line following robot.. and I'm using PID as the algorithm so I could only make sense of the PID if I could get the required input high or low at the right place...

Anyway, I would also need to change the threshold voltage accordingly depending on the surrounding environment that's why I need to vary the threshold voltage for the internal ADC of the PIC16F877A.. that's why I'm thinking if I want to vary the threshold voltage, I'll have to use the internal ADC and but if I use the external hex schmitt trigger 74LS14, I can't vary the threshold voltage, so I'll have to use the internal ADC but I duno how..

 

[blueroomelectronics]

You probably want a quad comparator if you're using 4 light sensors. You can adjust the trigger point unlike the 7414.

 

[dezmondngo]

You probably want a quad comparator if you're using 4 light sensors. You can adjust the trigger point unlike the 7414.

quad comparators? how does that work? exactly wad I need coz I'll need to vary the threshold voltage

 

[blueroomelectronics]

It's simply 4 comparators in a single IC. You could use 4 singles just more wiring.

The LM339 is a quad comparator.