Help with an AVR version of the POV Display

[sdudley]

Thanks everyone! (except for Stacy...)

[brad]

Aww I'm sorry. Thanks to you to!

[robertrndya]

hey Brad,

How are you? Its been a very long time. Please forgive me for not keeping in touch as I have been really busy over the past couple of months. Anyways, I have made my PCB for the POV. Everything is working . But not to my complete satisfaction.

I am trying to swing it by my hand, an idea I got from youtube. So i have put the PCB in a transparent plastic tube. I get the images displayed twice per rotation. Now the problem is that I'm not getting the images displayed smoothly, i.e. the image doesn't move round smoothly enough as it did when I had attached it to the ceiling fan. Maybe I need to play around with the OFF-Time Delay is it? Also the words that I display appear to be flickering a lot (It gets bright and dim). How do I reduce this flickering? If I increase the LED ON-Time it reduces the flickering slightly but then the entire image is not visible at the same time, i.e. now when I'm displaying "Google" I get to see it in this sequence - "Goog" ==> "oogl" ==> "ogle" ==> "Goog". So I can't just see "Google". What do I do about this?

Also I am trying to display the images at slow rotational speeds, since it can be very tiring to swing the tube fast for even around 3 minutes. The excel sheet data is of 32bits and 100 columns. I want to see the word "Google" span an entire half cycle of every rotation and at slow rotational speeds. Please advice me on this.

[brad]

Slow rotation speeds aren't good for these types of projects because in order to eliminate flicker, you need to be constantly updating the image and quite a rapid rate - we're talking at least 16 rotations per second, which is pretty fast!

Anything slower than that and you will see the flicker.

Now as for only seeing a certain amount of the complete word "GOOGLE" at a time it sounds like you are not allowing it to start at the start and go to the end when you are in your main loop.

also, it seems that when you are calling your data, it is starting from a different point each time. other wise it would always display something like "Goog" every single time.

unfortunately I haven't programmed AVR's so I am unsure of how to help you with your code. But you must be running some sort of loop in there to get it to work, just check the loop to make sure the loop is big enough for the entire text and that it starts from the same position everytime.

[robertrndya]

hi Brad,

Good to hear from you . Ok getting to the point, I do get to see "Google" entirely , but at times when "ogle" appears "Go" fades out . I'm guessing that's bcoz the rotational speed decreases , as its not possible to maintain a constant rotational speed with your hands.

Yes there are a couple of loops in the code and it starts addressing from the right locations since I have mentioned in the code the starting points of all the frames. I have kept a provision for upto 25 frames in the code, but practically I have tested with only upto around 9-11 frames max.

Ok now I understand why I see this flickering effect. I don't think I can attain such high speeds of rotation with my hands so I guess I'll have to be content with the flickering.

Anyways, so how is your new house? Fully furnished?

[brad]

Good to hear the the code is working

The house is coming along nicely, we still have a lot of work to do (and it is taking up most of my time lately) but it is good to see the results.

I will have to get some photos together and post them on the web

[robertrndya]

Brad,

I was just wondering if it's possible to create a GUI to generate my AVR source code depending on certain parameters that are fed in the program. I thought of this by looking at your GUI for LONG POV Converter which generates the source code for pic and then you have to paste it in swordfish. I was thinking, is it possible to generate the source code for the ATmega16L in a Notepad file so I can later copy and paste it in AVR Studio? I could ask the user to feed in parameters like the number of frames (images), the ON-Time Delay, etc. And how should I go about doing that?Should it be done in VB itself? Or is there any other software to do that?

[brad]

You certainly could make something like that. VB would be perfect for the job, but you could also use other programs like java or even xcode if you use a mac

[robertrndya]

Brad I am still facing a problem, they just don"t seem to be getting over. I use am Ni-Cd Rechargeable Battery (3.6V, 400mAh) to power on the poi. Now I don't understand something, when I fully charge the battery it reads 4.1V. Another thing is that when the battery is fully charged and I power on the poi, random LEDs turn ON (like as if displaying some garbage values). I have to turn it OFF and On a few times and suddenly the proper data is displayed on the poi. If I turn it OFF again and then ON it again then again random LEDs come ON. Then I have to OFF and ON it a few more times for the proper data to be displayed again. So what I do is when the right data is being displayed I keep the poi ON for some time (after sometime I turn it OFF and ON and see if it displays garbage values on startup or right data) until the right data is being displayed on power up. And when that happens I check the battery voltage and it reads 3.7V-3.8V. What could be the problem here? I have only question marks and exclamation marks on my head when I think of this problem. Please help me out on this....

[brad]

The only thing I can think of (that sometimes happens with PIC's) is that there is a reset pin on the microcontroller and if you don't disable it, it can cause strange results.

Have you checked that it is not resetting?

[sdudley]

The only thing I can think of (that sometimes happens with PIC's) is that there is a reset pin on the microcontroller and if you don't disable it, it can cause strange results.

Have you checked that it is not resetting?

What about a voltage (or current) regulator?

Stacy

[robertrndya]

Brad, the RESET pin is connected to PORT D, and I don't reset it in code. When I use a bench power supply to power the poi it works fine, but if I when I connect it to a fully charged battery (which gets charged to around 4.1V) it displays garbage values. when I reconnect it continuously suddenly it will display the right image. Again if I reconnect it, it will show me garbage values again.This happens only as long as the battery voltage is above 3.9V.

Stacy do you think I need to use a voltage regulator?

[sdudley]

Brad, the RESET pin is connected to PORT D, and I don't reset it in code. When I use a bench power supply to power the poi it works fine, but if I when I connect it to a fully charged battery (which gets charged to around 4.1V) it displays garbage values. when I reconnect it continuously suddenly it will display the right image. Again if I reconnect it, it will show me garbage values again.This happens only as long as the battery voltage is above 3.9V.

Stacy do you think I need to use a voltage regulator?

I could be wrong but it sounds to me like you answered your own question. Any bench power supply I have worked with are well regulated and the voltage / current are quite stable.

Have you placed an ammeter in the circuit while it is on the bench, or does your bench power supply display current? Find out how much current the circuit draws and then see if the batteries you are using can deliver.

Also, since the LED's are continuously turning on and off this might cause some sort of oscillation that can be easily fixed with a regulator or simply using a capacitor at the source as a filter.

I personally have no experience with POV's so I might be very wrong. It seems like a worthwhile experiment anyway.

Good luck,

Stacy

[brad]

Good advice Stacy!

I'd look at making sure you use a 7805 regulator (5v) which means you will need a battery of at least 6volts. also make sure you have filter capacitors (around 10uF)