Arduino Without Crystal

After making a “learning timer” on the Arduino UNO, Frank Carver thought about minimizing the number of tools and decreasing the overall size of the setup so as to bring down the cost. He aimed at turning the timer in a standalone project with its own battery pack, and enclosure, whereby he could transfer the exact circuit to a proto board. For this he made his own shrimp circuit following its official tutorial and started identifying what more changes could be done to further shrink it down.

Figure 1: Arduino without Crystal

Before proceeding further, it would be wise to note that a shrimp circuit is an Arduino Uno substitute which has a component cost of one-tenth of the original Arduino boards. There are kits available in the market with which one can make the simplest Arduino compatible circuit on a solderless breadboard.

Here is a list of the parts that were used in modifying the learning timer with a minimal setup:

Proto board
Wires
1 AVR ATmega 328P
8 LEDs
1 8-way 470 Ohm resistor pack
2 Momentary buttons
2 10K Ohm pull-down resistors for buttons
1 Piezo buzzer
1 100 Ohm resistor for buzzer
1 Pololu 5V step-up Voltage Regulator U1V10F5
1 SPST power switch
1 Double-AAA battery box
Enclosure

Rather than using any other minimal circuits, Frank decided to program the AVR ATmega chip and then plopped it into the circuit. This helped him in eliminating serial header, capacitor and resistor.

After that he considered to remove the crystal from the setup which was quite challenging. All the Arduino circuits usually utilize crystal at 16MHz but the ATmega chip works at 8MHz through an internal RC oscillator. Now removing the crystal meant changing the internal settings which are normally done set while programming the boot loader. After a few challenges and difficulties, Frank was able to program and compile the microcontroller.

Now the next step was to undertake testing using the simplified circuit which he built on another breadboard. Since his main objective was to check if the circuit works or not, he didn’t bother about the buzzer. Rather he just used LED array and buttons and had them wired up. For the battery, he wanted to make the project smaller and power efficient so instead of using a 9V battery and a regulator, he settled with a pair of AAA batteries and a 5V step-up board from Pololu. Even though this board is quite tiny, it does an exceptional job.

Finally, he soldered it to the leads of a battery box and plugged the free ends into the breadboard. Now the learning timer was ready to be put into an enclosure and it was running successfully.