That's a good idea, but I'm not a programmer so I would be going into mostly uncharted waters. Do you have a MCU that would work for me in mind?

The software for the circuit with the Mega8-P has already been written by someone who designed that circuit. There's much about the program that I don't understand. It's just a matter of time to understand it though. I just need to know the terminology and what they mean.

Thanks,


Mike

Lots of choices.

Lots of folks like the Arduino because it is all in one and there is really little to build, they even have snap in modules. But that might be a hindrance to your design.

I prefer the PIC. Easy to program but you need to build everything. Plus you will need a programmer. Around $60 for a real Microchip programmer which I highly recommend. You can find 3rd party ones for a bit cheaper but IMHO, not worth the small savings.


The Mega8-P is Amtel. I am not sure how popular it is around here. Pic and the Arduino seem fairly well supported.

 

I prefer the PIC. Easy to program but you need to build everything. Plus you will need a programmer. Around $60 for a real Microchip programmer which I highly recommend. You can find 3rd party ones for a bit cheaper but IMHO, not worth the small savings.

Are you talking about a hiring someone to program the chip? Sources?

I still need to know how much the controller can do. Can it replace the 8-bit counter (actually 7-bit) and all eight 4 to 16 line decoders? Can it drive the LED's or do I still need an external driver? I'll need to know how to wire the chip so it can be programmed. Since, it's not going to be connected to a computer for programming very often, can I use some kind of temporary connector?

Thanks a lot,
Mike

 

Are you talking about a hiring someone to program the chip? Sources?

I still need to know how much the controller can do. Can it replace the 8-bit counter (actually 7-bit) and all eight 4 to 16 line decoders? Can it drive the LED's or do I still need an external driver? I'll need to know how to wire the chip so it can be programmed. Since, it's not going to be connected to a computer for programming very often, can I use some kind of temporary connector?

Thanks a lot,
Mike

A "programmer" in Spinnaker's post is a device that lets your computer USB connect to the Microcontroller and transfer the code to the chip.

The Microcontroller can have timers (counters), comparitors, Pwm outputs, A2D converters, digital outputs and inputs (and more). I like to describe a Microcontroller as a chip where each line of input code corresponds to one and/or/NAND gate or other logic chip. Once you get used to using micros, you will think your boards are too empty and you are somehow cheating!

A good and common starter chip has been the PIC16F690. On board oscillator too.

 

Ah gotcha. Would you mind giving me a link to an example microchip programmer?

Ok, I need to figure out how many I/O pins I'll need. A 16 x 8 matrix gives me 128 pixels or pairs of LED's each controlled by it's own switching transistor. Won't I need an MCU with at least 128 I/O pins just for the LED's? Then, for the matrix, I'll need to control 16 columns and 8 rows. For the columns, I'll need four outputs and for the rows, I'll need 3 outputs. That adds up to 135 I/O pins. Or am I looking at this wrong? With 135+ I/O pins I could do away with the eight 4 to 16 line decoders thus saving space.

Right now I'm building just the counter circuit. Later, I'll do the matrix part. This is a rather big project for me and I just want to sort of do a proof of concept and do just part of the project. This will be just a light like a flashlight. I could put the control circuitry on one side and the lights on the other. I've never done a two sided board before, so this will be a first.

Thanks,
Mike

 

Look up
- multiplexing. You connect your array and turn a column or row on/off at a time. Then control individual LEDs in a column on/off by tuning a row on/off.

Many patterns can be made this way, you will need 16 + 8 I/o pins. Toy can flash quickly (alternating which are on/off at any given time. For example 4-digit displays of 7-segment numeral displays only require 7 + 4 pins. Each digit is updated 60 times per second or more and one digit it on at a time. It works and your eye cannot see the difference.

Look up shift registers also, to get a moving test effect (or rotating pattern). You can shift withing the Microcontroller or add a shift register chip to simplify the programming (but extra chips will add board complexity and weight). Extra lines of code weigh nothing!

 

The power supply for each LED is going to come from the counting circuit, so I don't see how I can use multiplexers to control that. In my drawing that I provided some time ago I have a switching transistor for each LED that turns it on. Maybe if you provide a drawing?

Thanks,
Mike

 

http://www.microchip.com/stellent/i...deId=1406&dDocName=en538340&redirects=pickit3

Microchip used to have one with the PIC18f45k20 mounted on a demo board. It came with a bunch lessons in C. It was very useful to learn micros. I am not seeing that option on the page I posted then again I di dnot look that hard.

Microchip has a wonderful parametric search tool.

http://www.microchip.com/ParamChartSearch/Chart.aspx?branchID=1012

An 8 bit chip would probably be enough for this project. Specifically I like the 18F family, They are supposed to be optimized for C though some would argue that that is just a marketing ploy.

 

You have many registers (variables) in the microchip and it can remember the multitudes of patterns you want it to repeat.

In the end, what is your goal? All kinds of different patterns of flashing lights or just an on-off of all flashing at the same time or something in between. Please describe.

 

Ok, sorry if I wasn't clear earlier. I'm planning two circuits here. One is a counter to flash each LED one at a time from 1 to 128 at the highest frequency I can manage so that they will appear to be on continuously rather than flashing, but only one LED will be on at any one time. The second circuit will control the matrix patterns. I'm attaching a drawing of how I see each 'pixel' being controlled. The outputs from the shift register or other circuit will go to all the LED's in it's row. Same goes for the output for the column controller. The two circuits will work together, with the goal being to save battery power. With only one LED on at any moment the current draw will be 100 - 150 mA plus whatever the draw is for each component. I'm always open to better ideas.

Spinnaker, thanks for the link. I like the idea of lessons in C. I sure could use a lot of examples.

Thanks,
Mike

 

I need help on understanding how to select a diode for the circuit shown in the picture. This circuit is from the data sheet for the (IS31LT3350) LED driver IC. What I understand so far is that the diode is there to help protect the IC from voltage spikes from the inductor. For my project the input voltage will be a regulated 12.2 volts and I'm planning on a current of about 180mA across two LED's in series. The LED's are high power requiring 6.1 volts and a maximum of 200mA to run. It was suggested I run the LED's at the current I plan to and feel or measure the temperature to make sure they aren't running too hot. They will be flashed at approximately 225 kHz, so they won't be on continuously.

Also, from the data sheet on diode selection:

For maximum efficiency and performance, the rectifier​

(D1) should be a fast low capacitance Schottky diode​

with low reverse leakage at the maximum operating​

voltage and temperature.

The higher forward voltage and overshoot due to reverse​

recovery time in silicon diodes will increase the peak​

voltage on the LX output. If a silicon diode is used, care​

should be taken to ensure that the total voltage appearing​

on the LX pin including supply ripple, does not exceed​

the specified maximum value.

Thanks,
Mike

 

How big is this rocket? I think you are making this much too difficult. By wiring all indicpvidually, you will have huge weight in wire, chips (transistors) and LEDs.

Find some SMD LEDs, an 11.1 volt lithium micro battery (like the hubsan micro quad copter uses. It will keep your LEDs on all day.

 

The whole point of this project is to learn. I'm an electrical engineer in training after all! Making this more complicated gives me more to learn. This will be going on a 20" diameter saucer and later may go on a 40" diameter saucer. Just by shopping for the parts needed I've learned a lot. What does each component need? The standard clock oscillators run mostly off of 3.3V and the counters require an input voltage outside the range of the oscillators. The solution to that is to use a Schmidt trigger inverter to get the output of the oscillators to a voltage the counters can use. As this project goes on, I'll probably start using the counters that come with many MCU's.

The power source will be a four cell 300 mah lithium polymer pack delivering 16.8 volts max. (actually two 300 mah packs in series) For the LED's I've selected a high power SMD LED and ordered a few to test them out. Since, the LED's are going to be flashing at approximately 225 kHz, I think I can run them around 150-180mA. I'm planning two of these LED's in series next to each other to make a brighter light at each pixel. I've also ordered a hand held infrared non-contact heat sensor for checking the heat output of the LED's to see if I'll need heat sinking. The LED's are just under 4mm square so I'm planning to mount them on circuit board strips about 6-8 mm wide by about 17 to 20 cm long. Doing it this way will help keep the lines of LED's straighter and make them easier to mount. For the wiring, I wonder if I could use those flat tape like wires? I don't know anything about them though. Or just use the smallest size wires I can without going over the amperage rating? Also, all the components will be surface mount so that should help keep the weight down.

Now, how do I select a diode for the circuit I posted earlier?

Thanks a lot,
Mike

 

Someone just explained to me that I can use an MCU to flash the LED's so that only one LED is on at any one time and also display a pattern. I just have to do it the same way that TV's display a picture. I think some of you tried to tell me that, but I just didn't see it. The faster the LED's flash, the brighter they will be. How high a frequency can an MCU flash them?

The way I've been doing it up to now just seems easier to me than programming it.

Mike

 

The sampling of LED's from Philips Lumileds arrived today. I hooked up one to a nine volt battery to see how bright it is. Just one of these puppies is so bright I needed sunglasses to look at it. I ran it at 6 volts and 66 mA, which is a little below what I was planning to run them at. I've added a photo of it, but it doesn't really do it justice. I was planning to put two of these next to each other to increase the brightness, but now I that I've seen how bright they are, I'm not sure I need to.

By the way, I don't know why the picture posted sideways.