Simplest Attiny85 based watch

We are used to see different kinds of DIY watches. Some of them try to stuff lots of functionality, other make fancy time telling format or simply mimic smart watches. But why not build a watch that only tells time in a simple manner. This Attiny85 watch is what it does. Schematic is very simple and straight forward – Attiny85 microcontroller, 12 LEDs, push button, three resistors and coin cell battery. Such simplicity allows building small watch shaped PCB where all components are fit to look nice and light. Since microcontroller comes with only 5 I/O pins (excluding reset), LEDs are connected using smart Charlieplexing method that allows saving pins for simple I/O tasks. The only shortcoming of this watch that time is counted using microcontrollers internal clock which may not be very accurate. As author states, clock is capable of keeping time within two minutes over 24 hour period. There are ways of calibrating internal clock source by manipulating internal registers, but in the end there is no point, as oscillator is dependent on many external effects like temperature,… Continue reading

Playing with bit-bang Ethernet on Attiny85

When going down into Ethernet or any other signal, you find that there is nothing more than ones and zeros. So practically any programmable device theoretically can send any information in any format. The only limit is RAM space, speed and signal conditioning. Cnlohr was able to squeeze Ethernet functionality in to small Attiny85 microcontroller. He was able to do so without external circuits – twisted pair was directly attached to microcontroller pins. This is really dangerous way to do, because Ethernet signal this way is forced to be tied to mcu ground. Ifthere is a DC offset in the line, it can cause damage. Normally there is a magnetics involved in signal line. Anyway this is great hack showing that anything is possible with minimal component count and small processing power. Attiny is clocked at 20Mhz and uses one twisted pair for network connection. IT is recognized as 10MBit Ethernet switch that can send hard-coded packets once one of couple buttons is pressed. To get 10MBit from 20MHz micro thee is an assembly language involved. As it is said,… Continue reading

Posture sensor helps you sit straight

If you spend lots of time by computer, you notice how hard is to sit straight. Over time you lean down, slide under the table or find other position that seems to be comfortable. Well there are two theories of this thing – first of all naturally your body tries to find best position to prevent you from pains and fatigue. Anyway prolonged leaning may result in back or neck pain. So siting straight may prevent from those problems. Bu how to control yourself when you are focused in to your task. You can always feel how you are sitting. Coretech Robotics suggest simple project that may help to sit upright by reminding you all the time. Device consists of ultarsonic sensor HC-SR04 which measures distance from your head. It is fixed to the backrest of chair at the head level. Attiny85 microcontroller monitors distance to the head and if distance increases meaning that you leaned, piezo speaker gives a signal so you could fix your position. Such solution may help you to develop a habit to sit straight as… Continue reading

Reducing interfacing pin count for nrf24l01

Sometimes we get caught in situations when we need direct solutions without figuring things out in more efficient manner. For instance microcontrollers and pin count. When we need more pins, we start looking for bigger MCU even if processing power is enough even if one additional pin would change the situation. So sometimes this is not effective to waste money and even design to get one or two additional I/Os. Some people may use I/O port expanders or shift registers to get more pins. But as Ralph shows we don’t always need head for obvious. There are tons of discrete electronics components around that may save the day. This time he suggests interfacing well known nrf24l01 RF module to small MCU like Attiny85 by using 3 pins instead of 5. So here it is a discrete schematic which does the magic. First of all Rf module is 5V tolerant except VCC must be powered between 1.6V to 3.6V. So a simple LED reduces VCC to save range. CE is another pin that can be tied to high. CSN signal was… Continue reading

LED Based Fireflies

This project is about a LED based asynchronous fireflies which were used as a Christmas project. The aim of the project was to make a low-power, low parts count module that can sense when it’s dark and then mimic the blinking patterns accordingly. For the project he’s using an Atiny85 along with an external clock which was programmed by setting external fuse-bits which is a conventional way to set clock source or frequency in almost all type of AVR’s A good things about the project is, it’s completely hand-made and that include the making PCB’s at home. To etch the PCB cupric chloride was used which is one of the quickest process to etch PCB but the time might depends upon the temperature. Also, to transfer the PCB design, from the computer to PCB, tone transfer method was used which is very impressive. An impressive project overall, but the complexity can be reduced if one uses in internal clock. Continue reading

Great knock box for Halloween

Halloween is a day when weird and scary things are welcome. So Kyle had this idea to make a knock box which would respond to knocks. Circuit is pretty simple and straight forward – Attiny85 microcontroller detects knocks by using piezo sensor. To make it reliable, he amplified piezo sensor signal by using MOSFET. Knocking back part is made of DC motor with shaft attached. Knocking pattern is recorded by using microcontroller timer. There are several modes preprogrammed for instance if 13 knocks are detected, then it plays “Adams Family” song using same piezo sensor as speaker. If 20 knocks are detected then box knocks randomly for 30 seconds. Otherwise box simply knocks back same patterns. A special attention is paid to box look. Lego skeleton and chains look great on it. Continue reading