Any experience with Touch Screens?

[Cosmic Software]

I have just come to the end of my Year 12 electronics project, and I have already started brainstorming ideas for what I can make next year.
I am a dedicated student, and am prepared to go much deeper than I need to to pass my exams.

I feel that a really neat thing to have would be a graphic LCD, with a touch screen. I have found this one on EBay:
http://cgi.ebay.co.uk/128-x-64-graphic-lcd-with-touch-microchip-pic-compat_W0QQitemZ280208504379QQihZ018QQcategoryZ36332QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Has anybody had any experience with an idea such as this with a Picaxe system, and most importantly, has it worked?
My ideas are changing all the time, and I have a couple of months before I must start, but I feel that it is never too early. I am soon to be going to JCB World Headquaters to talk to an electronic engineer there, who has agreed to give me support.
One idea is to use a strain gauge, but I do not know how to make a product out of this simple idea. I would like to use a touch screen to display information, and maybe have a menu to take the user through options of activating different outputs depending on the load.
I like the hardware side, but enjoy programming even more. I am not phased by a challange, but am aware that I must have whatever I make finished by a deadline.

Any ideas about graphic displays, touch screens, strain gauges, or anything else would be greatly appreciated.

 

[Dippy]

I've never done touch screen stuff with PICAXE, but there is a lot of info kicking around for the X-Y ADCing for resistive touchscreen. Maybe have a look at some of the touch-screen controller chips to see how they do it.

Also, if you can tear yourself away from Ebay, go to manufacturers sites of GLCDs+touchscreen and you can get DATA SHEETs which describe the physical nature of the resistive method - it's pretty simply really. The important thing is a good reference, good ADCing and speed of processing especially if you're planning 'drawing' on the screen.

Strain gauges will require amplification, you can't just ADC a strain gauge. Again there is plenty of info circulating on straing gauge amplifiers. Can be very expensive to buy, but there are circuit examples if you look with that ghastly Google thing.

Driving a Graphic LCD directly from PICAXE to get all the potential is a no-go really thats why Rev-Ed sell a kit.

 

[MurrayJ]

I am currently waiting for Dontronics to release the touch screen from 4D Systems. The non touch screen that they sell that I think will be similar to it is $179 so not cheap but it is 320 x 240 resolution, full colour, driver chip so only two interface pins (TX & RX) and has a micro-SD card slot to store pics etc so full featured.

Standard screen version to take a look at -

http://www.dontronics-shop.com/4d-Micro-LCD-320-PMD2-Display-and-Controller-p-16670.html

When they release the touch screen version (soon I hope) it will be "finger compatable" that is find the centre of a larger area such as your finger.

 

[eclectic]

Cosmic.

Wilf-nv did some brilliant work here.

http://www.picaxeforum.co.uk/showthread.php?t=5544&highlight=touch+screen

e.

 

[MartinM57]

Well the ebay listing says:
1. it's easily interfaceable
2. software and data sheets available to the winner
3. the breadbord connections don't look that complex

...I'd contact the seller, tell him you're very interested and will buy providing he supplies 2. beforehand (you don't have to buy even if he does send them - he can't neg you if there's no deal!)

 

[hippy]

"Easy interfacing" usually means easy to connect, not necessarily easy to control or use. Having software examples always helps but there may still be a lot of work to do in understanding that software and implementing it for a PICAXE.

I can understand wanting to go further than necessary to pass an exam for personal satisfaction but it would be ironic if you bit off so much to chew that others with much simpler systems passed while your far superior efforts were failed.

My recommendation would be to do two projects. Firstly a strain guage monitor which uses a standard HD44870 text LCD ( parallel or AXE033 serial connected ) and get that working and fully documented. That gives you something to hand in as finished and working. Don't alter that hardware once it's working !!!

Get that finished in under half the time you have and spend the rest duplicating the same again but with a GLCD plus touch-screen. If that works, brilliant, you have a prototype and a final project. If not, your prototype is the final project. Win-win either way.

Also, be careful when buying fom eBay. Not because of dodgy deals, but because unless what you buy happens to be something someone else is familiar with and used you are entirely on your own with making it work. What may look simple in theory can turn out to be difficult and even soul-destroying in practice - as I and others doing MMC/SD interfacing have found.

As it looks like you have a JCB Engineer to call on for help, one of the most useful things you may be able to get there is Project Planning help, and insight into where the biggest difficulties will lie. Before starting you need a project plan and timescale from which you will know when things have to be completed and how much work will have to be put in week by week. Four useful rules of thumb I've found from many years of experience -

1) Always add 50% to any time estimate, ie aim to finish 2/3rds of the way through the allocated time.

2) Last minute working can turn a near working project into a complete disaster and failure overnight.

3) Develop incrementally. Ensure you have something which can be passed off as fully working before adding something more, and make sure you can fall back to that position if needs be ( keep software, don't dismantle hardware ). Don't add enhancements or 'good ideas' until what you originally wanted is finished and working.

4) Documenting what you have and what you've done can take far longer than is expected. Always keep in mind what is being assessed and worth marks in passing the exam. A lack in one area can undrmine brilliant work elsewhere.

 

[BrendanP]

I use the Flexiforce load gauge and have found them good. They are cheap and rugged.

http://www.tekscan.com/flexiforce.html

Parralax have them in small quantities.

Its a plastic strip with a material sandwiched between two layers whos resistance changes with the application of pressure.

I managed to track down the op amp in DIP they recommend in their data sheet to use with the gauge. I'd be hapy to send you a couple if you can't find them in.

 

[Cosmic Software]

1) Always add 50% to any time estimate, ie aim to finish 2/3rds of the way through the allocated time.

2) Last minute working can turn a near working project into a complete disaster and failure overnight.

3) Develop incrementally. Ensure you have something which can be passed off as fully working before adding something more, and make sure you can fall back to that position if needs be ( keep software, don't dismantle hardware ). Don't add enhancements or 'good ideas' until what you originally wanted is finished and working.

4) Documenting what you have and what you've done can take far longer than is expected. Always keep in mind what is being assessed and worth marks in passing the exam. A lack in one area can undrmine brilliant work elsewhere.

I could not agree more with these four points, and I think that everyone should make a point of obiding to them. Unfortunately, I am saying this with the help of hind sight, hense why I will be spending some days of my easter holiday at school, trying to get finished the extra things I have put in, causing the whole project not to work!

Also, do not worry, I have never bought things from Ebay for use with electronics, but I have only recently realised what sort of stuff they sell. I usely buy from well known retailers, but they appear to be a lot more expensive!

You have given me a lot of interesting material to read, and I shall continue to do so. Thank you.

 

[Dippy]

Yes, buying from a 'proper' place can be quite a lot more expensive.
But, on the other hand, you sometimes get it next-day, and you get a warranty which will be honoured. That costs.

 

[MartinM57]

...I'd contact the seller, tell him you're very interested and will buy providing he supplies 2. beforehand...

So to practice what I preached, I contacted the seller. He was helpful and sent me the relevant data sheets, but no code (suggested I look around t'Internet for code examples).

The bottom line is that it is a KS0108B display containing a ADS7843 touch screen controller. If you Google for KS0108B you find threads like
http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=48528
...which show that just dealing with the display is a serious challenge, let alone integrating with the touch screen controller

I've no doubt it could be made to work, but even for a Year 13 project I think it's almost certainly too much of a challenge....

 

[Cosmic Software]

You could be right, but I have been doing plenty of research into the two seperate elements - the screen, and the touch pad.

If you check this link http://www.picaxeforum.co.uk/showthread.php?t=9125
it is about a very interesting chip that is made from a PIC, and the firmware on it allows for a Picaxe to be interfaced with a KS0101B GLCD driver chip. Although hush-hush, I have been able to locate this chip for £10 (rather than £50 as part of a kit from Tech Supplies), and it will easily interface with a cheap 128*64 GLCD (even from Ebay!), just so long as the screen uses a KS0108B driver.

The second part - the touch screen does appear to be a little more of a challange, and I require to do further research. The information in the link provided in an earlier post, to http://www.picaxeforum.co.uk/showthr...t=touch+screen used a brilliant idea using the 08M, and I was very taken with all of the switches. The touch screen section was also very detailed, however, I feel I need more information before I can be confident that I can do that.

I have yet to read the thread in the link above, but I feel confident that I will be able to drive a graphic LCD, and we will have to wait and see about the touch screen. I have done next to no research on strain gauges, but hopefully, they will not be too difficult.

Although it does not make the challange easier, my year 11 project could have passed for a A-Level piece of work, and my Year 12 project was too advanced for the teacher! It would be no fun to do an easy project. I also feel comfortable knowing that there is a great community here that will try to help me with any problem that I encounter.