Category Archives: Uncategorized

Counters with custom serial output

We recently made a modification for a customer that was such a great idea, I thought I’d post it here. They wanted to use our PRT-232 counter with RS232 serial interface but it was needed to interface to a legacy control software package. The software was originally designed to read data from a different serial measuring device. We modified the output of the PRT-232 to provide the text string the control software wanted to see on its serial port and the integration went smoothly.

It was such a useful concept we decided to offer it to anyone who requests. We will now customize any of the output strings the device generates for a nominal charge. That means that on an input switch transition, or specific level, we can output a string. e.g, input 1 goes active, it can send “Pump On” or if it goes inactive “Pump Off”
Or after counting to a certain value, we can output “Limit Reached” etc. It’s only limited by your imagination!

Of course, the normal behavior of the counter is unchanged: it will still count and report data as normal.

Measure temperature with AD592 and Arduino

The menu example in a previous post can easily be modified to conver the raw A0 analog reading into voltage. Since the Analog Devices AD592 converts temperature into a current proportional to absolute temperature, we can convert this to a voltage using a single resistor. By taking advantage of the Arduino’s 10-bit analog input, we read this voltage and convert to a temperature.

Here’s the updated code:

// Description:
// Simple menuing system for Arduino
// Demonstrates a menu with controls and
// data readback
//
// Communicates with PC at 115,200 bps 8N1
//
#define LED1 2
#define LED2 3

void setup() 
{
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT);
  Serial.begin(115200);
  menu();
}

void loop()
{
 int m = readMenu();
 switch (m)
 {
  case 1:
   digitalWrite(LED1, HIGH);
   break;
  case 2:
   digitalWrite(LED1, LOW);
   break;
  case 3:
   digitalWrite(LED2, HIGH);
   break;
  case 4:
   digitalWrite(LED2, LOW);
   break;
  case 5:
  {
    // VT100 reset cursor to end of menu (row 15, column 1)
    char resetCursor[] = {27,'[','1','6',';','1','H',0};
    Serial.print(resetCursor);
    double temp = analogRead(A0) * 4.9 / 10.0 - 273.1;
    Serial.print("Temp: ");
    Serial.print(temp);
    Serial.println("C");
    break;
  }
  default:
   break;
  }
}

// Waits in a loop until key is pressed
// then returns digit selected
int readMenu() 
{
 while (!Serial.available())
 {
   delay(100);
 }
 return Serial.read() - 48;
}


// Displays menu
void menu()
{
  // Clear
  char buf[] = {27,'[','2','J',0};
  Serial.print(buf);
  
  // Print menu
  Serial.println("\n\n\n\n\n");
  Serial.println("1....LED1 on");
  Serial.println("2....LED1 off");
  Serial.println("3....LED2 on");
  Serial.println("4....LED2 off");
  Serial.println("5....Read A0");
  Serial.println("\n\n Select 1..5");
}

Communicate to Arduino from PC

Although the Arduinos are great little controllers, sometimes you need to connect them to a PC to transfer data or control. One of the simplest ways of using a PC to control your Arduino is with a menu.

Menus have been used on computers pretty much forever. Back in the 80’s the green screen (green text on a black background) text menu was very popular. They persist to this day in some specialized applications.

In a nutshell, your PC will run a simple terminal program. Putty.exe is a great choice. It’s free, works great and supports the popular VT100 terminal control characters we will need.

The Arduino serial parameters are set to 115,200 bits/second, 8N1. Make sure your terminal program is set up similarly.
The example program turns on and off two LEDs and displays the raw data read back from the Analog0 port

Here’s the program:

// Description:
// Simple menuing system for Arduino
// Demonstrates a menu with controls and
// data readback
//
// Communicates with PC at 115,200 bps 8N1
//
#define LED1 2
#define LED2 3

void setup()
{
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT);
  Serial.begin(115200);
  menu();
}

void loop()
{
  int m = readMenu();
  switch (m)
  {
    case 1:
      // Turn on LED 1
      digitalWrite(LED1, HIGH);
      break;
    case 2:
      // Turn off LED 1
      digitalWrite(LED1, LOW);
      break;
    case 3:
      // Turn on LED 2
      digitalWrite(LED2, HIGH);
      break;
    case 4:
      // Turn off LED 2
      digitalWrite(LED2, LOW);
      break;
    case 5:
    {
      // VT100 reset cursor to end of menu (row 15, column 1)
      char resetCursor[] = {27,'[','1','6',';','1','H',0};
      Serial.print(resetCursor);
      Serial.print("A0: ");
      // Read Analog 0 input and display data
      Serial.print(analogRead(A0));
      break;
    }
    default:
      break;
   }
}

// Waits in a loop until key is pressed
// then returns digit selected
int readMenu()
{
  while (!Serial.available())
  {
    delay(100);
  }
  return Serial.read() - 48;
}

// Displays menu
void menu()
{
  // Clear screen
  char buf[] = {27,'[','2','J',0};
  Serial.print(buf);

  // Print menu
  Serial.println("\n\n\n\n\n");
  Serial.println("1....LED1 on");
  Serial.println("2....LED1 off");
  Serial.println("3....LED2 on");
  Serial.println("4....LED2 off");
  Serial.println("5....Read A0");
  Serial.println("\n\n Select 1..5");
}

 

When you run this, you will get a menu with 5 options. We demonstrate how to position the cursor on the screen using escape commands. Look at the code that prints the value of A0 on the screen for an example.

Menuing is a simple but effective way to get your PC and Arduino talking to each other.

Duplicating an existing item

Copying an item that is already on the market is a topic that continues to come up no matter what kind of manufacturing business you have.

The guys running machine shops, for example, are very familiar with people walking in off the street wanting a special washer, or bracket made. Often they are very upset at being told that the doohickey they could purchase at WalMart for $20 will cost hundreds or thousands to make. Why does this happen?

Let’s say you broke a part for a lawnmower. It’s a very simple piece of metal with three holes that is bent into a Z shape. It looks like a 5 minute job.

So you walk into a sheet-metal shop and ask how much it would cost to have one made, since you can’t wait a week for a replacement to be shipped. They shop foreman looks at it and says $500.

Why does it cost $500? Well, someone has to take that part, measure each dimension, measure the distance of each bent section, the offsets to all the holes, measure hole dimensions, material thickness, etc. Then the raw metal stock has to be retrieved from inventory, marked out, cut to size, drilled. The bender has to be set up, metal bent, edges deburred, etc. And that’s assuming that the shop even has the free time to get to it within a  reasonable time and that no jobs in progress have to be stopped. Under the best case, it could easily take half a day to make the first bracket. Of course, the next 500 could be made in the next half day now that all the design and setup work is done, but you only need one, so that doesn’t matter.

Much easier to just order it online for $15 + shipping!

It’s no easier in our world of electronics. In fact, it’s complicated by the fact that most of what we do involves the invisible aspect of software. A seemingly simple item that has a parts cost of $10 and sells for $100 could have $20,000 of engineering time behind it to create the first unit. Sure,  as a hobbyist you could copy it and do an awesome job and in the end it only cost you $10, but that ignores the cost of your time. If you’re doing it for fun, who cares about accounting for the time? The problem comes when you need someone else to do all or some of the work for you. Even without the overhead of a large engineering firm, that $100 item could still end up costing you $10,000 to make the first unit.

What does all that extra money pay for?

  • Documentation: how to build the next 5,000 units after that first one is done
  • Packaging: designing the enclosure it goes into and where the pushbuttons and LEDs go
  • User interface: does it have a display? Should multiple languages be supported? Is the flow from one screen to the other smooth and intuitive? It’s really easy to build something for your own use, but much harder when it has to be usable by a wider variety of people
  • Parts selection: which components should be used? Who to buy them from? Is anything critical about to be discontinued?

This is only scratching the surface. The point is that very often, asking to duplicate the functionality of a professionally designed item will require an equally professional designer and there won’t be any cost savings. Unless you need something customized for your needs, it is almost always far less expensive to buy an existing item off the shelf.

So, if you do need something specially built, how do you go about it?

Well, in an ideal world you’d have a complete set of requirements, or a detailed specification. In the real world, you typically only have an idea of what you want and need the details filled in.

So, the engineer you’re working with may need to know the answer to questions like:

  • Do you need just one, or thousands?
  • Will it use battery power or plug into a wall outlet?
  • Does it need to fit into another assembly?
  • If it measures something, how accurate does it have to be? More accuracy than needed can be expensive!
  • Will it be outside and need to be protected from the elements, or in a nice, clean office environment?

Developing a brand new product, or even a variation of an existing one, is a collaborative process. As you discuss your needs, you may find out that there are many small details that are actually important, but you haven’t had the opportunity to think about before.

In our prototype-building work, we come across this quite often. In the process of discussing a need, often the client realizes that there’s something off the shelf that could be modified instead. And it will cost a lot less than a custom design!

Arduino Programming: About time

Time is probably the most commonly controlled process variable. Timers are all over the place in industrial control. Odds are, if you need some type of timer, no matter how strange, you can find it off the shelf.

Now, many of these timers used a chip usually referred to as the “555.” The LM555 originally made by (I think; someone will correct me) National Semiconductor was a very versatile device, but it was at the heart of many time-delay relays, short timing circuits, etc.

So once upon a time, if you wanted to build a basic timer, odds are you would wire up a 555 into a circuit. To build a handful, or just one, you’d use a perf board,

perfboardmaybe you might use wire wrap or even dead-bug construction (my favorite!)

deadbug

It would be time consuming,but maybe you had no choice because the timer had some weird requirement that no off the shelf timer had, or needed to fit into an oddly shaped space.

What does this have to do with Arduinos? Well, you can program any timing sequence into an Arduino. Say you want the heater on a commercial ironing board to come on for five seconds when the operator lowers it, a 555 does it easily. If you want the heater to come on for five seconds and when the board is raised again, a fan to blow for 10 seconds to cool the clothing, the 555 can still be used. Maybe you need two of them. But now, the Arduino becomes an easier solution. Whether you need one time sequence, or dozens, a single Arduino can be programmed to do it. When you factor in the labor of wiring a circuit board with the 555, the low off the shelf price of the Arduino makes it even more attractive.

This is the wonder of the time we live in: an off the shelf microprocessor board is now inexpensive enough to be used for logic replacement.

Amazing

Arduino Programming: stuff we forget

This post will probably grow over time as I add suggestions from you guys. I see a lot of posts online from Arduino enthusiasts who want to build one thing or another. It’s easy to think of which Arduino version you need and the sensors, actuators, etc. The problem is that we forget all the small, incidental things and those costs can add up. When you’re making up your Bill of Materials (BOM), it helps to remember all this “extra” stuff you might not think of right off the bat so you get a good idea of what it will all cost.

So, what do makers/builders often forget?

  • Power. You need a power supply if you’re not planning on keeping your project connected to a USB port. And sometimes even if you are, you’ll need extra power to drive that motor, or multiple supply voltages because you can’t/won’t use a regulator
  • Enclosure. Is it going to be outside? Probably need a NEMA4-rated box. Even if it’s kept inside, a pretty enclosure is a great way to finish up your project and make it look professional.
  • Wire. Yep, something as basic as wire can really add up, especially if you need multiple gauges or ratings
  • Connectors. Round is better. Drilling holes is easy even with cheap tools. Making square, trapezoidal or just plain weird shaped holes is not. Well, not unless you have a machine shop at your disposal. If you do, maybe we can help each other!
  • Tools. Can you drill all the hole sizes you need?

Trimmable setpoint voltage divider

Let’s say you’re using a comparator like the venerable old LM339. You provide a setpoint “reference” and an input. If the input is below the setpoint, the output is clamped to ground. If the output is above the setpoint (plus any offset voltage of the comparator, of course), the open-collector output floats. Normally we tie the output to +5V if we want a TTL level output as we are often using the comparator to send a signal to a digital or microcontroller circuit. With me so far? OK.

The classic voltage divider is a good choice for a setpoint if it only needs to stay constant. But what if you need a variable setpoint? Simple, use a trimmer, trimpot, variable potentiometer, whatever you wanna call it. Now you can change the voltage of the setpoint. But wait a minute. If we have a regulated 12VDC and use a trimpot, even an expensive multiturn, it can still be difficult to set that voltage to within a millivolt. After all, a 10-turn pot with 12V at the input is still 1.2 volt per revolution, so with 360 degrees per revolution, you’d need fingers precise to almost 1/3 of a degree to set it to within a millivolt. Possible, but difficult.

Like most things, there are multiple ways to skin this particular cat (I can only write this while Lefty and Poncho are not in the room…).

20150424_194031

In the olden, golden days, engineers with beards and slide-rules used verniers that geared the output down, so one turn of the knob might only be 1/10th turn of the potentiometer on the output.
vernier

This makes it easier to adjust, but those things are $$$. Gotta be a cheaper solution. Sure, use a voltage divider. Remember the divider can take an input voltage and give you a smaller output, but if we make the divider variable, we can make it so we only vary it by a small amount. So instead of trying to adjust a 0-5 volt range with a potentiometer, we can design the divider so we only have to adjust a 0 – 0.1V range with the same pot. Much easier!

vdiv

Say Vin is 12V, R1 is 10k and R2 is 820Ω. Vout is then 0.91V. If we insert a 1k potentiometer between R1 & R2,that means that the output can now vary about that point.

divider

So, how does this work? Let’s assume the pot is all the way in one direction, the voltage divider is then 1,820÷11,820 x 12 = 1.85V

with the pot all the way in the other direction, the output is 820÷11,820 x 12V = 0.83V

Nice! So now our trimpot only has to control a span of about 1V instead of a span of 12V. With high-resolution A/D converters and digital inputs, these basic techniques aren’t  used a lot these days, but they are still useful to have in your toolbox.

Now go design something!

Sensors for counting objects

In order to count anything, we need to detect it first. This usually means some kind of sensor. The sensor used will typically provide a signal that our counter can read. Most such sensors actually function as a type of switch because their output terminals are closing a circuit on the counter electronics that causes a count to increment.

The simplest sensor used to count objects is an actual physical switch. Microswitches are switches with very sensitive contacts: a light touch is all it takes to register the presence of an object. Often microswitches are made with levers to reduce the force needed or to have a greater reach.

lever-switch

 

One common application for this type of switch is in coin counters for arcade games. The coin falls through a slot,  tripping the lever as it rolls past the switch. The main advantage of microswitches is their low cost and reliability. A disadvantage of this type of counting sensor is that physical contact with the switch is required and the force required to trip the sensor can affect the object you’re counting.

Another common sensor type used as input to counters or object detectors is a photoelectric switch. This optical sensor detects the interruption of a beam of light, often invisible infrared light. For example, to count boxes on a conveyor belt, an emitter, typically an infrared LED shines a focused beam of light across the belt. When the beam is reflected by an object passing by on the belt, the detector sees the returned light and closes a circuit and this sends a pulse to the counter module, updating the count of items going by.

photo

Optical sensors have the advantage of not requiring contact with the switch, but may not work well in dirty or dusty environments where the optical signal may be blocked. Also, this type of sensor used for counting reflective items can be “fooled” by multiple reflections, causing an inaccurate count. In this case, a through-beam sensor, where the item must pass between the LED emitter and its detector, is often more reliable.

Magnetic sensors, as their name claims, detect magnetic fields. They are very useful when a non-contact sensor is needed in a dirty environment where light may be blocked.

 

Now that we’ve got sensors to detect the items, our PRT232 counter module is the ideal interface to do the actual counting. We can make modifications to the basic counter, such as a display, or special RS232 signal outputs,

Arduino Programming: Cycle timer

Sometimes you want an operation to repeat periodically. Say you are building a parts washer that circulates cleaning fluid around the dirty parts. The cleaning cycle might run for an hour and in that time you want the circulation pump to run for 10 seconds, stop for 5 seconds for particles to settle, then run for 10 seconds and repeat for an hour.

We need a timer. The type of timer that does this is called a Cycle Timer because it repeats a specific timing cycle and it’s pretty easy to build a cycle timer with an Arduino and a little bit of software programming. We’ll need an Arduino (any kind, from any manufacturer will work), a power supply, the power driver circuit, and the “load” which in this case is our pump.

Let’s get started.

// Which pin to use to control the load const int OUTPUT_PIN = 1; 
// Total number of cycles 
const int NUMBER_OF_CYCLES = 10; 
// On time per cycle in milliseconds 
const int CYCLE_TIME_ON = 500; 
// Off time per cycle in milliseconds 
const int CYCLE_TIME_OFF = 200; 

void setup() 
{
 pinMode(OUTPUT_PIN, OUTPUT);
 digitalWrite(OUTPUT_PIN, LOW);
} 

// Run the timer 
void loop() 
{
 int cycles = NUMBER_OF_CYCLES;
 while(cycles-- > 0)
 {
    // Turned timed output on
   digitalWrite(OUTPUT_PIN, HIGH);
   delay(CYCLE_TIME_ON);
   // Turn timed output off
   digitalWrite(OUTPUT_PIN, LOW);
   delay(CYCLE_TIME_OFF);
 }
 // Hold forever
 while(1);
}