Touchscreen setup

Tiano-MSP430 based TouchScreen Piano

Touchscreens..huh.. They are all around us..Phones ,tablets, phablets and now even laptops. Most of them have a capacitive touchscreen where the change in capacitance at a point is used to sense it and then perform the corresponding action. Capacitive ones are multi point sensing. They sense more than 2 points and hence we get those pinch to zoom features etc.

On the other hand , almost archaic version on touchscreen is the resistive version. That are pretty easy to interface with almost any microcontroller with an ADC. In this project i did over the weekend i tried to interface a touchscreen ( resistive one..) ,available at mobile repair shops in Delhi with a MSP430G2553 (Although MSP430G2231 would also do)  to make a piano.

Touchscreen setup

Pre-requisites: The touchscreen may not be easier to get. I got mine from a mobile repair shop in LR. It is a 4-wire Touchscreen, pretty common with horribly thin contacts that took a lot of patience to solder.There is a lot of literature available on Touchscreens on the internet. I found two app notes that were best. First one from Atmel , that explained the working of the touchsreen in a pretty clear way and one from TI that some what helped in the software part.

You must read the atmel one ( atleast the first few pgs to get how it works). Its essentially a resistive voltage divider. The value of the touch point is determined by the ADC value read.

formula

From the illustration above(borrowed from TI App Note). One can easily see how the co-ordinates are read. In order to find out, what wire on your touch sreen corresponds to X and Y meshes. You can use a multi-meter first to measure the resistance between pins ,usually the alternate pins belong to same axes. in my case it was X-,Y-,X+,Y+  then to differentiate between x and y , one probable method will be to power the touchscreen i.e. giving the drive voltage and then find out the voltage at any other terminal w.r.t. ground and see whether is changing horizontally or vertically in your reference plane.

CAUTION: Be careful about the current while powering the touchscreen externally!

After this coding part is pretty simple. For the algo refer to page no.7 on the TI App Note. If you plan to run your end application on a battery and you have hard-coded the co-ordinates and the Vdrive is sourced externally i suggest that you sample the Vdrive as well . If you are using  microcontroller pins to supply Vdrive then this can be neglected.

I have a desire to learn to play music but unfortunately due to my low patience levels , i have failed to keep up. 😀

So, i made this Piano using the MSP430 Launchpad and a touchscreen along with a speaker. The code algo is pretty same as TI App Note Suggests and i encourage the reader to code it himself . Any difficulties can be discussed. It uses the tone library i posted earlier to generate the solfeggio.

Here is the shaky and horrible video i made:

Cheers! 😀

DSC05610

Reverse Engineering an Automobile Fuel Gauge using MSP430 Launchpad

I have been keeping my hands off the blog for a while after the previous post.. I had exams at university. But in the meantime i had some time to get my car`s faulty petrol/gasoline Gauge Indicator Changed. I got the old one and as usual i tried to reverse engineer the gauge with all the simple tools i had. Technically, Its a ” Floating type Liquid Level Resistive Transducer’ (You can trust me on that..I am a student of Electrical Engineering 😀 ). So basically its a variable resistor much like the LDR or a Potentiometer. The one that i have is a pricol make for Maruti Suzuki Cars. You can have a look at the pictures below. DSC05612

DSC05610

Using the TI MSP430 Launchpad i decided to sort of simulate how the Indicator would actually work in real situations. So i pulled up the ADC Pin on the MSP430G2231 using a 220 ohm resistor and connected the fuel gauge indicator as in the set-up picture you can see below.You can use any platform you like arduino,stellaris etc. all you need to do is read the ADC value and produce a corresponding brightness for the LED and when at a low level raise a low fuel alarm which in my case is the RED led. I used Launchpad as it has Two on-board LED`s while my arduino has only one ; additionally i was lazy enough not to wire another led to arduino 😛 .

DSC05614

On measuring the resistance across the fuel gauge i found that when at the lowest position it has a resistance of about 112 ohms and at the maximum it was about 7.2 ohms. On the sticker pasted on the top its mentioned-” Do not connect direct 12 volts”.Which is pretty obvious because since the resistance is low, the current will be pretty high.

12/112=0.1amps

but on full scale its about 12/7.2 ohms=1.67amps

This current is pretty high and will surely burn the coil.

So we now know why the sticker is there! 😀

The program simply blinks the red led when there is low fuel. Rest of the time the intensity of the Green LED is proportional to the amount of fuel thereby producing a variable DC voltage which can be sensed using a voltmeter quite similar to the one fitted in the car console.

TL;DR

Watch this video:

Thanks and Regards,

IndianTinker 😀

post3

Tutorial: Using the Internal Temperature Sensor on a MSP430

The value line series (g series) chips that come with the MSP430 Launchpad are pretty cool and has almost all the required peripherals to work with..The best on is ( for those with the newer version v1.5 or later, that comes with pre-soldered Male headers ) MSP430G2553, It has pretty much everything to get you started. Since, I was a little curious i bought the MSP430 launchpad quite a while back..Mine came with a g2231 and g2211..Of which G2231 is the one that has an ADC. The MSP430 boasts of an internal temperature sensor which is probably new to me who has worked earlier on AVR. So, I went on and tested the ” <Accuracy>”  of the sensor.

For you to proceed you need to have this (user`s guide) and refer the pages 559-564.

post1

So setting the bits in the INCHx to 0b1010 (i.e 10 in decimal) the MSP430 allows us to use its internal temperature sensor.

We have chosen the reference voltage to be 1.5V in order to have an ADC Value that is more or less immune to the Voltage Fluctuations.

The code is as follows:

#include<msp430g2231.h>
void tempInit()
{
	ADC10CTL0=SREF_1 + REFON + ADC10ON + ADC10SHT_3 ; //1.5V ref,Ref on,64 clocks for sample
	ADC10CTL1=INCH_10+ ADC10DIV_3; //temp sensor is at 10 and clock/4
}
int tempOut()
{
	int t=0;
	__delay_cycles(1000);              //wait 4 ref to settle
	ADC10CTL0 |= ENC + ADC10SC;      //enable conversion and start conversion
	while(ADC10CTL1 & BUSY);         //wait..i am converting..pum..pum..
	t=ADC10MEM;                       //store val in t
	ADC10CTL0&=~ENC;                     //disable adc conv
	return(int) ((t * 27069L - 18169625L) >> 16); //convert and pass
}
void main(void)
{   volatile int temp;    //initialise
	WDTCTL = WDTPW + WDTHOLD; //stop..bow..boww
	temp=0;
	tempInit();//initialise adc
	while(1)
	{
		__delay_cycles(500); //wait and set break point
		temp=tempOut();           //read temp
		__delay_cycles(500);  //wait and set breakpoint

	}
}

Code is under this licence .  😀

So, when you flash this code using CCS the breakpoints need to be set(Not compulsory et`all). What breakpoints really do is that it stops the program there and allows you to see the value of the watch expression and then when you press the pause/play button again..it will run until the next breakpoint..Its a pretty cool feature..and many use it to analyse code behavior.

This is how you set a breakpoint in the CCS-Edit window:

post2

Just click on the bar next to the line number bar..(Currently highlighted in blue).

These are the results you get by setting the “Watch Expression” to the Temp variable..

post3

The temperature it reads is 23 Degrees Celsius..while my room temperature measured by a standard thermometer is  20 Degrees. which is a relative error of 15%. So, scientifically that`s not accurate..but i dont think that is what it is designed for..I think it is designed for just to give an “Idea” of what the temperature is about..So we can see if we are getting colder or hotter.

The code is pretty well commented and i find it self-explanatory..But still if you have any query ..I am just a “Comment” away!

You can also find the complete CCS project in this repo on github!

Cheers and Greetings!

Indian Tinker!

cd4511

TI MSP430 Dice( and other experiments)

7 Segmented Displays are pretty low tech and have been around for quite a while.They have a lot of wiring clutter with them..But still they are by far the most easiest(and cheapest) way to give out a (alpha)numerical output..I had interfaced 7segs with MSP430 a while back directly but owing to the low current capabilities of MSP430 the display wasn`t very good and clear . We were recently ‘taught’ about the BCD-7 segmented display in our semester..So i thought about interfacing the 7 segmented with the CD4511..This will save some precious pins and plus drive the 7 seg directly. The CD4511 IC can run from 3V Supply..So no power supply issues and the logic high(input) is about 2V which is also apt as on MSP430 we have this about 3.3V.

The datasheet is available  here

The only thing that was bad was the wiring clutter  has increased and there were (as always) a few loose connections.After a few minutes,I was up and running with the display.

The Fritzing Schematic is given below:

cd4511

Do everything according to the picture above for the code to run. If the Schematic is not clear..then refer to datasheet linked above.Everything has been done according to it..The LT(bar) and BI(bar) have been connected to +VCC and LE to ground.The display is powered from the ‘board’.

The connections (from the MSP430 end to CD4511) are:

P1.4 -D

P1.5-C

P1.6-B

P1.7-A

#define D BIT4
#define S BIT5
#define B BIT6
#define A BIT7

The code to drive the CD4511 “According” to the above config is:

void CD4511(int numb)
{
switch(numb){
				case 0:P1OUT&=~(B+A+S+D);
				break;
				case 1:P1OUT|=(A);
				       P1OUT&=~(B+S+D);
                break;
				case 2:P1OUT|=(B);
				       P1OUT&=~(A+S+D);
                break;
				case 3:P1OUT|=(A+B);
				       P1OUT&=~(S+D);
                break;
				case 4:P1OUT|=(S);
				       P1OUT&=~(A+D+B);
                break;
				case 5:P1OUT|=(A+S);
				       P1OUT&=~(B+D);
                break;
				case 6:P1OUT|=(S+B);
				       P1OUT&=~(A+D);
                break;
				case 7:P1OUT|=(S+B+A);
				       P1OUT&=~(D);
                break;
				case 8:P1OUT|=(D);
				       P1OUT&=~(B+S+A);
                break;
				case 9:P1OUT|=(A+D);
				       P1OUT&=~(B+S);
                break;
				default:P1OUT&=~(B+A+S+D);
				break;
}
}

Just to clarify :The code uses ‘S’ instead of ‘C’ because C was being used as an internal macro in the header file!

The video is down here..It first shows the simple counter..then the push to change count and then the Dice.
To get the complete source code..you can comment below..The comments are moderated so you email will not be leaked.
Thanks for passing by!
🙂
#Sorry for the bad cam! 😛