Tag Archives: sketch

ATtiny85 Bricked? No problem!

Messing with fuses may brick ATtiny85!

On Attiny85 (also on other Attiny__) chips from Atmel, I recently made mistake, not knowing exact ‘truth’ about how to set fuses properly, so that it work as expected. The problem is in online documentation and implementation in some of available programmers as is “Khazama AVR programmer”. Even online calculator is wrong – if for example you want to use 8 MHz and above external quartz crystal oscillator, then you should select CSEL = 1110, but calculator showing that three boxes should be unchecked (CSEL[3:1]), while last box (CSEL0) should be checked. THIS IS NOT TRUE!!! If you look in datasheet about Attiny85, then it is exactly 1110, but online calculators, and programmer showing confusing and contradictory messages about what enables or disables what. So, I made (not so short) video about this issue + how to ‘un-brick’ Bricked Attiny__ (in my case Attiny85).

Is there hope for bricked chip?

YES! Bricked Attiny85 simply does not accept ISP programmer, but it can be ‘rescued’ by so called “HV programming”, where high voltage is actually 12V to the reset pin (pin number 1 on Attiny85), then some weird commutation of +5V and +12V on the chip brings it into programming mode. Down below is diagram and sketch, which is not my idea, but rather I with to thanks and give credit to those people who designed it and modified so that we can rescue our favorite chips.


On the image above, there is credit to someone who made it possible, but someone else changed sketch slightly, so that it now works as is expected.

The sketch for Arduino nano:

Be careful about the “Fuse calc”!!!

You may notice that “Fuse calc” gives (for example) result of 1110 for external quartz oscillator, but boxes below are incorrectly checked! Pay attention to that. Here is my video and some conclusions about that:

Instead ugly 12V lead acid battery, consider buying this 5V to 12V step-up converter.

PWM modulation as DAC on Atmega328p

PWM or Pulse Width Modulation

It is good to have 8 ADC inputs on Atmega328p, of which last one is actually thermometer inside chip, but there are no DAC converter for making sound out of digital data. Tried one DAC chip, MCP4725, which is 12 bit DAC with I2C data transfer, but turns out that it is pretty slow even at 800 kHz I2C bus. That is because of something weird inside this chip, where time required for output signal to reach maximum, starting from zero is 6 microseconds, no matter what I do. So, I decided to use PWM as possible way to do DAC conversion.


How it works?

By using fixed frequency, but variable length of the pulses, it is possible to change output voltage from digital output (!) from zero to maximum voltage, depend of voltage which is applied to Atmega328p. If pulses are narrow, then after filtering by low pass filter (RC or LC filters) – output voltage is low. If pulses are wide, voltage is higher. So, in the case of 5V on the Atmega chip, if duty cycle is 50%, then output voltage is  2.5V.

How good is sound quality?

Not so good if PWM frequency is low. Also depends of how many bits are used. If 16 bit timer is used, in theory it is possible to use all 16 bits, which will give 65536 voltage steps, but then PWM frequency will be pretty low. For driving motors or LEDs it is not a problem, but it is problem for audio applications. Some relatively good quality for voice is possible by using 62.5 kHz PWM with 8 bit resolution on Atmega328p with quartz crystal on 16 MHz. That is because Fast PWM with timer(s) and divider of F_CPU/1 (no prescalling) require 256 counts, which can be calculated by formula: FPWM=F_CPU/256. In the case of 16 MHz crystal, this is 62500 Hz, or 62.5 kHz. This frequency is pretty good for voice audio, but not so great for music. But, this is trade-off of using inexpensive way to make DAC out of this chip.

Other way than using timer(s)?

Yes. I had problem making exactly 40 kHz for ultrasonic purpose, because of all frequencies at which PWM can work, neither one can be get by using dividers, and/or number of bit manipulations. So, I made an “PWM imitation” by using two delay loops (for (;;) ), where variable delay is obtained by changing number to where loop goes. For example: “for (i=0;i<32;i++);” together with the rest of the code gives me 12.5 microseconds, which is half of 25 microseconds needed for 40 kHz (1/25 uS = 40 kHz). There are two loops, where first one gives ON time, and second one OFF time. Sum of ON+OFF time gives duty cycle in steps depending of how much bites are used. Since whole process is relatively slow, I am forced o use just 5 bites, which is okay for voice audio. This mins that 5 bites gives duty cycles in 32 steps, from near zero to maximum (which in my case is not 100% but rather close to 80% due to other commands in the C code). One of this additional codes are ADC conversion and mathematics conversion from 10 bits to 5 bits. This just slow cycles enough so that it can’t reach 100% pulse width.

The code:

Note that I wrote “parametric speaker”, because this code is intended to do job, but I found many problems with sound quality out of ultrasonic speakers with this modulation. Still working on improvements. But, this code is good for exercise in advanced programming. Later on, I will make code for audio with PWM at 62.5 kHz for telecommunication purpose (voice over digital radio-modem). Here is video rant about this PWM stuff:


Arduino I2C Scanner

What is the I2C address?! Scanner please.

Do I need such scanner? Sooner or later, everyone stuck on some I2C device – unknown address. For example, on OLED display, there is jumper (SMD resistor with “000” – zero Ohms), and next to it: “IIC address eslect”, and two options, soldered at first one: 0x78, and can be selected another one by removing this resistor and soldering at second place: 0x7A. But, after opening example code for this OLED display, it does not works. Why?! Because it has address of 0x3C, not 0x78 as it is designated. So, here is simple sketch I found somewhere. Well known and simple sketch, but very useful:

You may use :

Most of the default examples uses 9600 bits per second, but sometimes I need it faster, so I made it “115200”.  If you have problem with your serial port (USB cable to your Arduino), then lower speed, it is up to you. Just be sure to select the same speed at Serial Monitor, bottom right corner. Else it will not work.


Instead making wiring diagram, I will just tell you that SCL and SDA of the device in question goes to SCL and SDA on your favorite  Arduino board.  Usually with numbers 4 and 5; SCL (serial clock) to pin A5 (or ADC5, or pin number 28), and SDA (seral data) to pin A4 (or ADC4, or pin number 27). Do not forget to power your device with appropriate voltage and connect ground wire. Usually it is 5V, but there may be exceptions.

It will give you info every five seconds, something like this:


Arduino altimeter

Altimeter: Another problem with losing data during lost signal:

Altimeter sketch, Tried to change library from VirtualWire.h to RadioHead.h, but memory on Arduino nano is already too much populated, working memory for variables. So… Don’t know what to do… OLED display take 1024 bytes (1 kB), maybe I should to consider different display?

Altimeter programming problemsaltimeter

Explanation about mistake in my test flight with altimeter.

Altimeter: some outdoor test is done with one big mistake…

This video is made before utilizing “second order temperature compensation” in sketch of the transmitter. It looks complicated, but it turns out that is actually simple to apply (or I become somewhat good in programming). 😀 What happens is that I set zero indoor where temperature is close to 20°C, but outdoor in early morning was just 7°C, which gives me error of about -6 meters. Now things are better, error is still present but no more than say – 3 meters. BUT (!), now this error is within ballpark of maximum -3 meters error if temperature changes dramatically, which in most situations is not the case. Problem may occur during winter time, when someone want to fly briefly, and bring outside “warm” quad with sensor at say 20°C, then begins to fly – when set zero on ground, fly, and back, on ground should be again zero. For this reason, give quad and sensor some time to accommodate to whatsoever temperature outdoor is. Sensor is temperature dependent, and between 20°C and maximum operating temperature of 85°C it has pretty linear reading. The problem begins below 20°C, and exponentially rise with lowering temperature. But, since we are not interested in correct atmospheric pressure, but rather correct measured altitude, such error of -3 meters (which is about 0.5 mb, or 0.5 hPa), is next to nothing if quad fly very high AND (!) in meanwhile temperatures drops drastically. Down below is sketch for Attiny85, which is now corrected with added additional math. In the worst case of temperature drop, error is no more than -16 meters at temperatures between -15°C and -40°C DIFFERENCE (!) between starting temperature and temperatured during flight. And, I doubt that anyone has actual will to fly on such cold and freezing butt temperature. 😀

Altimeter: transmitter under 3 grams! (2.75 g with antenna)


On this ‘remote’ altimeter, still need to add ISP connector with 6 wires for re-programming firmware. Just in case that something need to be changed. Else, it is under 3 grams, but as ‘features’ growing, it will be slightly above 3 grams. For example, this 1/4 lambda antenna is okay, but full dipole (1/2 lambda) is better for more range. Just need to finish receiver end, post it on this page, and test maximum possible range. I am hoping for 1 km or more, but will see. Also, not sure how it will looks like on the quadcopter. For rockets, there will be different version – one without transmitter, just recording max altitude in EEPROM, then red with some base station, but that is future plan. Or, maybe I will find some good and lightweight LCD display… don’t know… For quadcopters, it is good to monitor altitude dynamicaly – in flight, but for rockets… eh, it goes hight as it goes – no way to monitor it in real time.

Arduino Altimeter – first steps are done

Altimeter – Beta version works on 433 MHz, base station should be pressed “zero” to set zero of the vehicle (airplane, quadcopter…), and then it will calculate altitude by receiving data from vehicle to the base station. So far, I have some problem with OLED display and it’s library: it uses too much memory and some instability occurs when it is out of range and not used for longer period. Just need to see what may be done…


Download (PDF, Unknown)

Working day and night… not only this project, but other things as well. Just some short video:

On this video, pressure sensor MS5611-01BA01 is used. By clicking on this link, you will get datasheet if you are interested.

Another PDF file MS5611-01BA03, much detailed, where at pages 17, 18 and 19 – diagrams showing error in pressure and temperature measurements without applying “Second order temperature compensation”, where sensor below 20°C increasing interpreting pressure reading exponentially as temperature goes really low. This math correcting it as much as possible. Still some error remains, but with peak of about 1.8 mBar at temperatures between -15°C and -40°C. Without this, additional math, error at such temperatures are up to 28 mBar at -40°C. At some “normal” local atmospheric pressures of say 1000 mBar, error of 1 mBar equals 8.426 meters. As pressure goes down, this error goes down. So at very high altitude, where temperatures are low – error becomes less important. I will be more worried about LiPo battery, than about sensor.

Another changes

Changed way of displaying Actual altitude, and Maximum altitude reached, shown as A: and M: respectively. Both in feet and meters.


And got idea about barometric pressure (for altitude calculation), humidity and temperature of the base station. Later will be added another barometric sensor in the case of rapid change in weather, as is case past few days prior to rain. This second sensor together with humidity and temperature will make it almost complete meteorologic station, mobile one. Just missing wind speed, and few other parameters, but so far – it looks much better and more “rich” than before. 😀 To read meteo-data, just switch into second position, while altimeter continues to measure altitude and “remember” maximum reached. MaxAlt is done by simple code:


I wish to have better and bigger display in order to show all data at once instead changing “pages” on OLED, but here it is, what it is… New Nextion display ordered, just waiting to arrive.

Some old rant

Rant about altimeter, old video, scroll down for more info.

Work on Altimeter. Just need to add some display on receiver side, check again everything, test range and add something.

First codes for TX, test phase

So far it works as a “Packet Radio” on 433 MHz, the ISM frequency. Transmitter and sensor + Attiny85 is chosen so that whole sending device will be under 3 grams – good for any vehicles. Unfortunately, it can’t work as altimeter not as vario + altimeter as planed. The main problem is in receiver side; if I combine relative slow transmission, some 24 packets maximum, tone sounds crazy and has delay. So, later version of the Arduino altimeter will has switch to chose altimeter or vario with the same circuit. For now, I did only altimeter, everything else will be added later (for those who found this page before end of test or beta phase of developing).

Some errors corrected

In the example below, initial idea is used from Arduino Vario by Rolf R. Bakke. He made initial code in such way that pressure is with OSR (OverSampling Ratio) for pressure, which is 4096 , so that resulting RMS (Root Mean Square) is 0.012 mBar (the lower number – the more precision). But (!), because higher OSR requires longer conversion inside MS5611 sensor chip, this value requires delay of 9.04 ms (minimum 7.40 ms, typical value is 8.22 ms and maximum value is 9.04 ms), So, for sake of ‘safety margins’, he uses 10 ms delay for pressure reading, since ADC need this time in OSR mode 4096. But, he uses OSR for temperature of just 256, which is equivalent of RMS of 0.012 °C, which is okay for vario, but not for altimeter – numbers jumping up and down too much. He probably made this decision because vario should be very fast, and already present delay of 10 ms + 1 ms at another command, adding more delay may result in too slow vario to be useful for sailplanes or gliders. The more samples per second – the faster the response.

Vario is one thing, altimeter another

For this reason, I changed call function from “D2 = getData(0x50, 1);” to “D2 = getData(0x58, 10);”, which has RMS of 0.002 °C – much better temperature correction data (six time better temperature correction than in the case of OSR 256, which gives RMS of 0.012 °C), but ten times longer to read (instead 1 ms, it needs over 9 ms to complete oversampling). The same as above for pressure, I am using 10 ms for good measure to prevent error(s). Anyone who want to experiment, try change from 10 ms to 1 – terrible error occur, instead some ‘reasonable’ pressure of say 1010 mbar, there is nonsense, something like -2.5 mbar. ADC converter just can’t cope with that speed, and reading sensor ends in big, really big error.

Why then in Attiny85 code is 1000 instead 10 ms?!

This is mystery to me. I had no time to investigate, but I suspect that library ‘VirtualWire’ resulting in such strange thing. It is actually good to have tens of microseconds (!) instead of thousands, or 1 ms (1000 µs = 1 ms). Since this strange thing is there, anyone who want to change some delay should multiply wanted value by factor of 100 to get proper delay in milliseconds. For example ‘delay(1000)’ usually means 1 second, but in example below, it will be delayed just 10 ms. So, for whole second, it should be ‘delay(100000)’. There is some limit, where delay can’t be set to high value, but instead should be used ‘for/to/next’ loop for more delay, if needed. For example 12 seconds: “for (i=1;i<=12;i++) {delay(100000)}”. This will be delay of 1 second repeated 12 times – 12 seconds. But, this is out of scope for this altimeter.


Base station

Base station has OLED display for now, because found only this one. Later will consider make various options; OLED, TFT, numeric LCD, graphic LCD…

Just need time… First code for base station is here (sorry, no diagram yet, working whole night – for those who found this page in the meanwhile):


The same MS5611 sensor is used in Arduino variometer. And it is cheaper than ever on Banggood.com

This is all for now

Come back soon, will be updated… Escpecially diagram and videos… Spring time requires hard work in my backyard, but also I did now and then some job for money, and this is main reason of delay of everything.