Mini POV device

I recently made a POV (Persistence of Vision) device that is used to display text, I call it mini POV. One reason is because it's small, and second is because it's very quiet. All I have it saying right now is "HELLO". The device is controlled by a PIC16F628A, the display is shown on a 10 segment bar graph display. when the test is shown, it's only using 8 segments of the bar graph, I left the other two out when coding because I just wanted to see if this thing actually worked. Here are some pictures:


Here is a video:

That is great! I have always wanted to make a POV device, but I never started . Looks like you are getting the hang of using PIC and not the Basic Stamp. How is it going? Do you like it a lot more?

Are you thinking of adding some sort of encoder so the PIC knows how fast it is spinning? That way you could stabilize the text. If I made one I would probably use a stepper motor that would be controlled by a different AVR/PIC and have a set RPM that the AVR/PIC on the arm would know, but it would probably be easier with an encoder as you already have the DC motor running nicely.

Do you have a regulator hidden under your PCB or did you manage not to fry the PIC with 9V?

Justin

I do have a regulator hiding under the board. I am going to add an encoder to the board. It's going to be the typical IR sensor and nail encoder. The nail is on the table, the IR sensor on the board, every time it passes the nail, it shows the text. I'm also trying to get the battery off of the motor, even though the motor is strong enough, I'm still trying to make it go faster, so I will need to decrease weight. What I was thinking of is having the PIC and the battery together, then have 3 wires brush against 3 spinning leads, on for +5V, one for GND, and the other for communication to the other PIC. But it's not working great with that idea so far.

I do enjoy PIC's way more than the basic stamp, I will soon start on using AVR, maybe try out the Arduino board or something.

My next POV will be mini 3D POV, but I will still be working on this one to perfect it.

I would leave the battery on the arm. Using brushes is a tricky thing to get right. You often loose connection for a split second if there is any imperfections on the brush. Also If you are using an encoder why do you need to use another PIC?

If you want it to go faster first make sure everything is perfectly balanced. Balance it like a set of helicopter blades. Something like this. That will help quite a bit if it was not balanced before. I was also told with my helicopter that it also matters where the center of gravity is on each side and they should match up, but I would not worry about that for now. If that is not enough try a smaller battery if you can find one or a larger motor.

Justin

Everything is perfectly balanced, it is the most balanced it can get.

The reason why I was talking about 2 PIC's, was because one(the one on the arm) will control the display, and the timing with the encoder, and the second one will have the program to send data to the display PIC to output the message/image. I'm working on a new one right now, I the idea down. But I'm not sure if I'm going to use a separate controller board.

You could go wireless.

Why not just have one PIC do it all? I could see if you want to have the display generated with your computer, but other then that I would just use one PIC for simplicity. If that one PIC does not have the power you need why not just put the second PIC on the arm as well?

Justin

First of all, I'm not that great with IR stuff. Do you think you can draw out a schematic for a good IR encoder the sends a digital signal? Because mine works, but it only sends out analog, which the PIC can't detect, and I'm already using the analog comparator pins for something else.

What level is the input from the encoder? If it goes over 2.7V (for 5V powered PIC I believe) then it will register as a 1. If not you can always add a comparator. Something as simple as this will work.



You can flip the + and - pins if you want the out put to be inverted.

Justin

The level for the input is 5V, going to a photo transistor, to a 2N3904 transistor, then to the PIC. I don't think it works that way with the PIC, since it's not doing what I told it to. And what circuit are you using for that encoder? a TLC272 or a 386 amplifier thing?

Check what the PIC will see with the IR light blocked and without the light being blocked with a multimeter. If the range is somewhere between 0V-1V for on or off and 2.8V-5V for the opposite then it should work fine as the PIC should register 2.8V as a 1 and under 1V as a 0. I have never used an encoder but I did use a photo-interrupter and a comparator to sense when the projectile in my coilgun passed though the barrel. When I did that I used this photo-interrupter and this comparator. You should note that that comparator is in a SOIC package. If you need a DIP one make sure it is push-pull type, it makes things easier.

Here is the complete circuit with the photo-interrupter. The Digital OUT would connect to a PIC's input. I had it switch an IGBT on and off.



Justin

EDIT: I forgot to say that you may be able to forget the comparator and just connect the PIC to the IR transistor. Just check and see if the change is large enough. I had to use the comparator so the IGBT would turn on and off fast.

I'm currently working on my next prototype POV, I have the IR sensor working on a breadboard without using the diagram you told me, just connecting the IR receiver straight into the chip, with a 4.7K Ohm resistor sending a ground signal to the pin. The one I'm working on is not the 3D POV, the 3D POV might be my next one, once I obtain enough LED's, maybe RGB.

That is good to hear. You usually don't need a comparator for the PIC to get the signal. When you say 3D POV do you mean the ones that are like balls? You can buy cheap RGB LED on ebay. That is where I get all mine, from Hong Kong.
Justin

When I mean 3D POV, I mean something different from what you're thinking.

Regular POV top view:

O -motor
|
|
|
0 - LED's

Regular POV side view:

___________^^motor^^
0 -LED
0 -LED
0 -LED



The 3D POV is different


3D top view:

O motor
|
|
0 LED's
0
0
0


Side view:
_____________^^motor^^
0000
0000
0000 - LED's
0000

The 3D POV will be an LED matrix spinning fast, thus when programmed right, it can display 3D objects.

I just finished making the display board with the LED's on it, I'm working on the controller board. Is there some kind of code or chip I can use to get two PIC's to communicate to each other through one wire? I'm not talking about EEPROM and anything else, no wireless. I'm basically saying, can I get a PIC16F628A and an 18F4620 to communicate with each other, by connecting one pin on the 16F, with one pin on the 18F. I know there's a way, but is there a certain library built into MikroC or MikroB, or one that I can download to do this?

As far as I know there is no way for a PIC to communicate with another PIC bidirectionally with one wire. If you need both PIC to talk to each other then your best bet is to use I2C. You only need three wires, ground, SDA, and SCK. On the other hand if you only need the control PIC to talk to the display PIC you could use serial, but you would still need two wires, ground, and Tx. The Tx of the talking PIC connects to the Rx of the listening PIC.

You could cook up your own creation for bidirectional one line communication, but it gets complicated as you have to know when to talk and when to listen. It is like a two way radio. If you try to talk at the same time as the other person you can't hear what they say. This is called half-duplex. Full-duplex, like SPI, allows both sides to talk and listen at the same time, but SPI uses three pins while I2C uses two.

Justin

I'll try bread boarding this idea first before I make the final ideas. All I really need to do is to get the controller PIC to communicate with the display PIC. The display PIC has no information to send back, and I can't think of anything that is needed to send back.

I know MikroC has a built in library for USART as I have used it. You just need to set them up the same, baud rates, stop/start bits, etc.
Justin

The progress so far on the new POV device:

1. I call it super mini POV (super means that it has extra stuff)
2. The code is going to be written in MikroC
3. I have the IR sensors working on the display board
4. The controller board is almost complete (This controller board is also my 40 pin PIC experiment board.)
5. I have an idea how to transfer voltage and data while the device is spinning

If you have suggestions to make this thing any better, tell me. I might release the code when I'm finished if anyone wants to view it.

Glad to hear it is coming along. I loved MikroC, I own the dsPIC version and a LV24-33 board. Both I don't use anymore due to the fact that MikroC does not work on Linux. Now AVR is all I use.

Let me get this strait. You are going to have your display board setup so you can talk to it like a serial LCD, just send it text/pictures and it will be displayed. The controller board will be sending the information to be displayed.

It sounds like you know what you are doing. What was your idea on how to transfer power and data?

Justin

That is exactly right on how I will transfer data, it's the easiest way through one-wire.

My idea for transferring power and data. I just happen to have a roll of copper tape when doing this, (that's right, copper tape), anyway, I cut an index car and glued it around the circular piece of plastic that holds the POV arm. I then got the copper tape I mentioned earlier, and wrapped three rows on, the first row is +5V, the second is GND, the third is COM. Now that I have all that set up, I had to think of something that would make contact with the copper tape strips. What I did was get three pen springs, put them on cotter pins, and let them brush up against the strips lightly just enough to keep in contact when spinning.

Hopefully this will turn out great.

Just make sure that the track that the tape is on is as centered and smooth as possible. At high RPM the brushes might lose contact for a split second causing the PIC to reset. Make sure you put a big capacitor on the display boards power line.

I also have copper tape . In fact I also have aluminum tape. The sticky part of the tape is not conductive I tried to use it to make an easy connection to a battery. I ended up having to tape the copper exposed side to the battery.

I was wrong... There is a way to use only one wire. It is a lot more complex then serial though. Check it out.
Justin