The long awaited part 2 of this blog post has finally arrived! But first, a video, in case the whole “reading” thing isn’t your bag…
I forgot what the original inspiration was but what I’m ending up with is a working binary clock on a custom printed circuit board. Ultimately, this project will involve fiber optics inside polished cement for a unique time piece but we’re not there yet… Here’s what I learned so far:
Bit shifters
A binary clock needs 20 individual blinky things and the arduino has less than that, so I needed to figure out a way to create more individually addressable outputs. The solution I found is a the 74HC595N chip that can turn two inputs into 8. In fact, you can wire them in series and they can provide you with any number of outputs in multiples of 8. I decided to use one to drive the hours display, one for the minutes, and one for the seconds.
Keeping time
While you can make a timer with just an arduino, it is not very accurate and it has no way to keep the clock going if you unplug the power. I used a rtc1307 chip which is designed for just this purpose. It keeps time accurately and uses a small battery to continue keeping time when the power is disconnected.
Removing the arduino
Eventually, since I wanted to end up with a single circuit board, I didn’t want to have to plug anyting into an arduino. Once again, the internet is a wonderful resource which allowed me to figure out how put only the arduino components I needed onto a bread board. I can upload the code onto the chip by putting it on an arduino, and then pull it off of there to mount it directly onto the breadboard.
Code
The clock can be set to one of 4 modes: display time, set hours, set minutes or set seconds. There are two buttons. One button toggles between all the different modes, while the other increments the count of the hours, minutes, and seconds when they are in their respective mode.
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#include <Time.h> #include <Wire.h> #include <DS1307RTC.h> //Pin connected to ST_CP of 74HC595 const int latchPin = 8; //Pin connected to SH_CP of 74HC595 const int clockPin = 12; ////Pin connected to DS of 74HC595 const int dataPin = 11; //Pins for setting the time const int button0Pin = 5; const int button1Pin = 6; // Variables for debounce int button0State; int button1State; int previousButton0State = LOW; int previousButton1State = LOW; long lastDebounce0Time = 0; // the last time the output pin was toggled long lastDebounce1Time = 0; // the last time the output pin was toggled long debounceDelay = 50; // the debounce time; increase if the output flickers int button0Mode = 0; // object to communicate with RTC tmElements_t tm; void setup() { // Setup pins for the shift register pinMode(latchPin, OUTPUT); pinMode(clockPin, OUTPUT); pinMode(dataPin, OUTPUT); // Setup pins for manual time setting pinMode(button0Pin, INPUT); pinMode(button1Pin, INPUT); } void loop() { RTC.read(tm); // button 0 can be in display time, hour set, minute set, and second set modes. // if( button0Mode == 0){ timeDisplayMode(); } else if( button0Mode == 1){ setHourMode(); } else if( button0Mode == 2){ setMinuteMode(); } else if( button0Mode == 3){ setSecondMode(); } // // mode switching // // Just after a button is pushed or released, there is noise where the value returned is 0/1 random. // debouncing consists of reading the incomming value and, if it has changed, storing the time the change was noticed. // It then continues to check and if after a certain amount of time (delay), it reads the input value and it is still the changed value // noticed before, then it means that an actual state change happened. int reading0 = digitalRead(button0Pin); // this only happens when the input value is different from the last time the value was read if (reading0 != previousButton0State) { lastDebounce0Time = millis(); } // we only enter this loop if the returned value hasn't changed in a while, which means we are not in the noisy transition if ((millis() - lastDebounce0Time) > debounceDelay) { // if we are in here, it means we got two similar readings. if (reading0 != button0State) { // if the two similar readings we got are different from the stored state, we must have changed button0State = reading0; if(reading0 == HIGH){ button0Mode = (button0Mode+1)%4; } } } previousButton0State = reading0; delay(100); } void timeDisplayMode(){ int sc = tm.Second; int mn = tm.Minute; int hr = tm.Hour; digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(sc,3)); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(mn,3)); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(hr,2)); digitalWrite(latchPin, HIGH); } void setHourMode(){ int reading1 = digitalRead(button1Pin); if (reading1 != previousButton1State) { // reset the debouncing timer lastDebounce1Time = millis(); } if ((millis() - lastDebounce1Time) > debounceDelay) { if (reading1 != button1State) { button1State = reading1; if(reading1 == HIGH){ tm.Hour = (tm.Hour+1)%24; RTC.write(tm); } } } previousButton1State = reading1; digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(0,3)); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(0,3)); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(tm.Hour,2)); digitalWrite(latchPin, HIGH); } void setMinuteMode(){ int reading1 = digitalRead(button1Pin); if (reading1 != previousButton1State) { // reset the debouncing timer lastDebounce1Time = millis(); } if ((millis() - lastDebounce1Time) > debounceDelay) { if (reading1 != button1State) { button1State = reading1; if(reading1 == HIGH){ tm.Minute = (tm.Minute+1)%60; RTC.write(tm); } } } previousButton1State = reading1; digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(0,3)); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(tm.Minute,3)); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(0,2)); digitalWrite(latchPin, HIGH); } void setSecondMode(){ int reading1 = digitalRead(button1Pin); if (reading1 != previousButton1State) { // reset the debouncing timer lastDebounce1Time = millis(); } if ((millis() - lastDebounce1Time) > debounceDelay) { if (reading1 != button1State) { button1State = reading1; if(reading1 == HIGH){ tm.Second = (tm.Second+1)%60; RTC.write(tm); } } } previousButton1State = reading1; digitalWrite(latchPin, LOW); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(tm.Second,3)); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(0,3)); shiftOut(dataPin, clockPin, MSBFIRST, setTimeBits(0,2)); digitalWrite(latchPin, HIGH); } // create binary value for each digit of the hour/minute/second number // offset represents how many bits are used for the tens. int setTimeBits(int n, int offset){ int n1 = n%10; int n0 = (n-n1)/10; return n0 | n1<<offset; } |
Schematic and board
Once the breadboard was working, I set out to sketch the circuit in Fritzing. While it’s not quite as intimidating as EAGLE cad, I ended up using the latter after running into some limitations with the former (I don’t remember what they were). There was a lot for me to learn there but, in the end, it’s conceptually pretty simple: all the pieces have to be connected together correctly. It’s just another way to represent the circuit. Once that was done, I started with the board. I laid out all the components and let the software automatically figure out how to create the correct traces.
One cool thing is that if you choose the correct electronic components in the software, all the size and shapes are properly represented when you are designing the board. It’s a huge pain in the ass to sort through all the libraries of components, though, specially when you don’t know what all the specs mean.
Manufacturing the board
Super simple: just go online and find a service that will manufacture them. For this project, I used oshpark.com and dirtypcbs.com, which allow you to upload your designs right out of EAGLE cad. After a few weeks, you get your board in the mail, ready for you to solder the components on. I order my components from mouser.com, which allows you to save a collection of various components into a project specific list. Again, finding the right components amongst the tens of thousands they have available is really time consuming and annoying. But now, I have my parts list so I never have to go through that again if I want to solder up new versions of the board. The list of parts in included in the download file at the top of this page.
The ugly truth
If you were paying attention, you no doubt noticed in the preceding paragraph that I used two board manufacturers. That is because the first board layouts I had printed actually had shorts. I suppose it’s probably not that uncommon, but it’s really frustrating to upload your designs, order the boards, wait for them to be delivered, spend all this time soldering the board to find out it doesn’t work, and then it can be challenging to figure out where the wires are getting crossed. In the end, I spent about $150 on boards and parts that ended up not working. I guess that’s the cost of learning… My first two board designs were ordered through Oshpark, and the minimum order was 3, for about $50. The third order was done on dirtypcbs and was $25 for 10 boards. They feel cheaper and took forever to get delivered but you sure can’t beat the price.
