delay generation

Hello,

Please create a separate discussion (or question) for each separate issue you have. There is less chance it will be lost in a discussion with different topic and higher possibility that someone will notice and help.

To the subject:

First, you haven't provided any schematics, so make sure you know how is the LED connected to a PIC pin and whether it sources or sinks the current for your LED.

Second, according to what you wrote, I don't think you have problem with the code toggling an LED itself, but somewhere else in the code, handling / responding to the detection of a touch. Helping would be easier if we could actually look at the code.

what you probably have in pseudocode:

     if touch_detected > turn LED on

          else turn LED off

what you need:

     if touch_detected > toggle LED

hello..

I am working with capacitive touch sensor with pic18f microcontroller using CTMU.

i want to toggle the LED with capacitive touch sensor..means  when i touch the sensor that time i want  LED in ON State till the next touch,when i again touch the sensor that time i want LED in OFF state till next touch...

for toggling this LED i used following syntax..ie

LATDbits.LATD1 = ~ LATDbits.LATD1 ;

LATDbits.LATD1 = ! LATDbits.LATD1;

and also

LATDbits.LATD1 = 1

LATDbits.LATD1 = 0

but using all above methodes LED is turning ON when i touch the sensor,and turning OFF when i release touch sensor..

i dont know which methode is use for this operation...

what should i do for this operation ?

plz help me...

thank u......

The old fashioned way used coils of wire as a delay line. The length required is 300mm per nanosecond * the velocity factor of the conductor used.

These were superseded with digital versions.

http://au.element14.com/webapp/wcs/stores/servlet/Search?pageSize=25&st=delay+line&catalogId=15001&categoryId=800000000312&langId=43&storeId=10184

You can also use 74HC5555 or its inspiration the NE555 timer.

ok thank u david..

i think time delay in microsecond is suitable for this unit..

i will try to maintain that boudaries...

thank u so much...

I think you got the CTMU wrong. There is a current source, but the voltage to be measured by ADC can't be higher than Vdd of the PIC. (It is just a regular ADC, with +Vref as Vdd or something else smaller than Vdd.) I hope no manufacturer will design a chip with such self destruction capability

Your calculation has to count with all the variables. You can set the current value of the current source, you can create variable time delay. The capacity is something you want to measure by measuring the voltage (charge) created by the current source for the time delay.

To your question - with 1 ms delay, you will just measure Vdd, which is meaningless and gives you no answer about the measured capacity.

Try to stay within Vss and Vdd boundaries otherwise your measurement makes no sense.

Thanks David..

see in CTMU there is one internal capacitor inbuild

when we set EDGSTAT1 bit in CTMUCON register that time internal capacitor start charging using internal 5.5uA current source

after that we have to wait some time for charging thats why we need time in microsecond,then we dissable EDGSTAT1 bit in CTMUCON register ie stop charging of internal capacitor

so i was asked the question,becoz i want to know what happen if i use time between charging and discharging capacitor is microsecond ?

Can i use the time delay in millisecond using timer interrupt for CTMU ?

according to calculation when i consider time in millisecond that time voltage is increasing

ex.

I = 5.5uA

T = 1ms

C = 30pf

V = 183.3v

and  183.3 V on ADC pins for microcontroller  is not possible..

plz share some tips for me..

Thank you...

Hello,

I am sorry, but I don't understand your question. What do you mean by

Can i use the time delay in millisecond using timer interrupt for CTMU ?

I personally haven't used CTMU unit in PICs, however, I've quickly gone through the referenced application note AN1375 and 18F46K22 datasheet. It is up to you, how you implement the delay (a timer, fixed length loop, ...).

(BTW, I recommend reading application number 47. and 48. in that application note. Seems that engineers wanted to accompany the useful text with some fun )

hello...

I am working with Capacitive sensor using CTMU in pic18f46k22..I am refering AN1375 App note for CTMU..

this microcontroller having CTMU unit for capacitive sensor.in CTMU registers , i am using 5.5uA internal current source,and 14us delay which is generated by timer interrupt for CTMU.

calculations....

c = 30 pf

I = 5.5uA

T = 14us

v = ?

according to mathematical calculation

v = (I*T)/C

v = (5.5uA * 14us)/30pf

v = 2.56v

my question is ,

Can i use the time delay in millisecond using timer interrupt for CTMU ?

plz help me, i am not able to understand the accurate calculations..

thank u..

How precise and how accurate?

Accurate timing comes down to a time base and synchronization.

You can accomplish these tasks depending upon your requirements.

Please share them if you want a good answer.

DAB

hmm...

Really u have lots of experience in Embedded..

nice to meet u..