Need Help - Childrens Interactive

Projects General Guidance
1

I'll start by saying I know nothing about arduino.
I have been tasked with creating a push button LED display that says 78°F and when you push a button it would say 26°C. This is an interactive that demonstrates to children what temperatures are required for certain animal medical procedures. I have googled around and it seems arduino would be the easiest way for me to do this, but I have no clue what to buy and have no clue how to program. Can someone help me out? My intention is not for someone to do my work for me, I could learn Arduino but usage would be very rare in my field. Thanks in advance.

Brian

2

Where is the 78 degrees coming from, room temperature or user input? It sounds like an Arduino Uno, HD44780 LCD display and a few buttons will do. Assuming the degrees you want are user inputted you could have two buttons to go up and down in temperatures and a third button to switch that number between temp ranges.

Edit: Just noticed you mentioned using an LED display. How large would the display need to be?

3

78 is the teperature it would be if it were real, I'd like it to always say 78 or 26. Would just need a single button to switch between farenheit and celsius. The ideal size would be about 1" high by 2 13/16" wide. Our "real" temperature controllers that we use have (2) 2 digit LED's (LDD-C812RI is what I think it is based on a google search) and are bright green, so trying to make it look similar. I have an old housing from a broken controller that I was hoping to mount the new LED panel in. Looks like I can make everything I need it to say with the 4 digit LED, just don't know how to do it.

4

Since you are using set data, you really don't even need to use a microcontroller at all. But, using the arduino, check out this library: Arduino Playground - SevenSegmentLibrary, you will have to modify that because it will not have the patterns for the degree symbol or F and C.

An LED display is just 7 LEDs with a common anode or cathode (Seven-segment display - Wikipedia). The display you cite is a common cathode type.

You need 7 330 ohm resistors. These will go between the a-g segments and the arduino. On the arduino, you wire all a's to one pin, all b's to one pin, and so on. Then for each display, you put the common cathode to an individual pin.

You set your a-g outputs as you want them for one display and then drive the common cathode for that display low to turn on the LEDs.

These are the patterns you need:
7 = A,B,C

8 = A,B,C,D,E,F,G

2 = A,B,G,E,D
6 = A,F,G,E,C,D

F = A,F,G,E

C = A,F,E,D

DEG = A,B,F,G

You have to cycle through all displays repeatedly. You do it fast enough that the eye doesn't see the flicker. Set a toggle in code for your button to keep track of the two states (F and C) and then just light up the displays.

You would need 12 pins total (7 for the segments, 4 for the digits, and 1 for your switch.) If you need to save on pins, you could just hardwire the displays with your two different states, and turn them on using only 1 pin for each state (so 3 pins total.)

5

If you can make use of these types of displays wiring it quite a bit easier. 0.56" 7-Segment Backpack | Adafruit LED Backpacks | Adafruit Learning System

6

thanks for all of the replies and ideas. I am going to attempt a parts list and post for feedback. Should I buy from some place like mouser, etc.?

7

I have no particular input on place to buy the stuff. Mouser is one place, digikey another. I guess it depends on what you need to buy. You mentioned that you have a non-working unit, right? Why not just repurpose that?

8

I would love to repurpose the existing unit, however, the manufacturer will not give me the PCB schematic, and without that, I have no idea where to start. I played around with it, and make the LED's light up, but not sure how to get around the on board processor, etc. I would be happy to upload photos of the PCB (if that is possible on here) if someone wants to have a go at reverse engineering it, it's beyond me.

9

You can get around the processor by just removing it, or cutting the voltage supply to it. If you can already light up the LEDs, that's all you need. It probably even has a nice power supply built in that you could use. I don't know if it's ok to post the PCB pics or not. I guess I don't know why not, it's just a picture of an object.

10

Ok, here are 2 pics of the controller. Can you make sense of it? Power in is 110v and is the 2 terminals on the left in the picture LED 2.

LED 1.jpg
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LED 2.jpg
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11

The only components you want are a simulated display, right? And to use the built in power supply of course... The picture is too blurry to see actual part markings, but it is about what I would expect. That big cap near the display would be your logic power rail. It is probably 3.3 or 5v. The striped side is gnd and the other side is positive. You can trace from that to a easily solderable spot. The pins marked S4 looks like it has 5V and GND on the outisde pins.

I see a microcontroller with the marking scraped off (towards the front) and what is most likely an ADC chip (towards the back). There is a small eeprom next to the microcontroller which probably has tuning values saved in it (probably what is wrong with this.) I don't know what the little 8 pin chip is next to the relays, but it is probably an instrument amplifier for the temp probes.

There are four transistors on the bottom side of the board by the display. These would be driving your digits (one for each digit across the common cathode.) There are also 4 little 6 pin packages. Again, I can't read the markings, but I bet they are hex fets used for driving the LEDs. Also on the bottom side of the board is a little capacitor right under S2. If you trace that to the CPU pins on the top, that is your power Just lift all pins going to both sides of that cap. If we knew what the PN of the CPU was, we could just set RESET to be on all the time and that will get rid of it. Are there any visible markings on it? Of course, you could always just remove the CPU completely.

12

Obviously I can't see the traces on the display, but it looks like from left to right (bottom side picture) you have the four common pins of the display. Then 8 pins for the segments. They would all be connected together. and the last three pins are for the LEDs.

13

BTW, pin 8 on the little eeprom is VCC and Pin 4 is ground. Just find all the spots those pins connect to on the CPU next to it to remove power from the CPU.

Looking at where the pins are going, it looks like an ATMEL 89C52 or other 44 pin 8051 variant. That's pretty common in this kind of stuff. Reset is on pin 4 which is going to the blue resistor pack. I also see the serial port is pinned out to those big through-hole pads beside the eeprom.

Here's the datasheet:

That is the TQFP/PQFP version.

14

Retroplayer, thanks a ton, sounds like you understand the board. I am going to take it home with me and get a better picture of it with a real camera vs. the cell phone pics I posted. I roughly understand what you are saying but will have to research some of your terminology to fully understand. The processor has info on it but the print is too small for me to read un-aided, better pics will fix that. It sounds like i will be able to re-use this, which will be a huge win for the exhibit and the interactive! I will want to pick your brain some more once I get rolling on this thing, if that's ok with you.

15

That's fine with me. Always willing to help. I am positive that CPU is an 8051 derivative. I followed the rest of the pins and it all matches up. So no need to read the print. These all have the same pinouts. Just lift pin 4 and connect it to VCC.

BTW, I have never seen that board before. I just have a knack for reverse engineering stuff troubleshooting and recognizing circuits. Been doing this a long long time. If only I can wrap my head around programming as well as I would like!

16

If you use shift registers to drive the leds then you only have to feed them a bit string to change the display. Search on shift register at the same site, 1 shipping charge for 1 order.

If you will lots of these then use the Arduino for development but use stand-alone chips for the end product.

What I don't get is why not include a cheap thermometer? Then they could use the same unit in the experiment itself.

See 78F, hit a button to see 26C -- you might as well use 2-sided flash cards, they will teach just as much just as well for far less unless the real lesson is to waste money and electric on trivial flash. Oh well, that seems to be the way things have headed for decades now anyway.
Waste, waste, waste, it must create jobs somewhere to waste!

17

I wondered the same thing (without the rant, of course) but I assume that the OP has his reasons. He mentioned temperatures of animals. So, the actual temperatures displayed must correspond to something simulated, not real.

OP, mind going into a bit more detail about your project? Perhaps there is more that we can help with.

18

Thanks for the replies guys. I work for an Aquarium. We are building an exhibit that teaches the public what is involved in animal care. The specific piece of the exhibit where I will use my altered temperature controller will be a realistic life sized model of a fish surgery set-up, aimed at kids. As you can imagine, any type of surgery requires close temperature control, 78degF for the specific species being modeled. Wasteful would be tempering the water in the exhibit, since it isn't "real". I could just put a sticker on the controler that shows 78, but wheres the fun in that? So, I'm putting a little effort into making it as real as possible. With all that being said, hopefully you understand a little more of what I am trying to do. If I go Arduino, then i have to write the code which i know nothing about. If all I have to do is some soldering on the unit I have, then seems easier with no out of pocket other than a button for switching between displayed values.

Retroplayer, I have attached another photo, is this what you are suggesting?

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19

Yep. That is pin 4 on the CPU. You will need to connect it to jumper it to VCC once you lift it to keep the processor in reset. Pin 8 of the eeprom is the bottom right pin in that picture (note the dot which indicates pin 1 - and when no dot is present, you can use the slope on the one side of this type of package to find pin 1.) I was mentioning pin 8 only to help you loacte VCC. Since there is a serial port on those 4 through-holes (on the right side by the eeprom) I bet one of those will be VCC. There should be VCC, GND, RX, and TX. So for whatever circuit you throw in there, you can tap off 5V supply from that point. To find it, just check for continuity between pin 8 and one of those through holes. That blue cap will also have VCC on one side and GND on the other. Another good place.

Again, you could just completely remove the processor if that's easier and nothing else will interfere with the display.

You will have to decide whether to use an arduino or not. The advantage to using the Arduino is that you get to learn to code as well as allowing you to add more features if you get in there and start having fun (it gets addictive!) Because of the way this display is wired up, you will not have an easy time doing what you want to do without the Arduino. This type of display is expecting the characters to be drawn sequentially which means your circuit would have to be designed to to step through several states. That will end up being pretty complex and quite a few parts. I suggest just installing an arduino in there. The seven-segment library linked in this post is designed for the way this display is wired up. The only thing it is missing is the degree symbol, which can be added.

Don't be intimidated by starting an Arduino project. Before you even start, think about what you want to do just like if you were making a recipe. You have steps that have to be taken in a certain order, and there may be tests (like taste for salt at step 2) performed that determine output (add more salt). And there may be interrupts (like the oven timer going off) and delays (waiting for one step to finish cooking.) That's really all programming is. You do it every single day.

20

Wait... those two LEDs on there next to the display. Are those the indicators for Cels and Fer? Could you provide a picture of one of these units in action? I was going to post how to modify the library and such, but maybe you don't need to even do that.