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I thought I’d do another quick teardown, this time of a photo keyring we had lying around for a while.

Four screws later and we’re in.

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Following from Part 6 we moved to the ATtiny44A, using voltage dividers/level shifters to communicate with the SRAM when the ATtiny44A was at 5 volts. In this part we will add some code to calculate the baseline reading when no load is connected and modify the way our USB data transfer works by not emulating keyboard any more so we can transfer the data faster.

Here’s how the breadboards look at the moment.

Calculate baseline reading

Now that I’ve tested that everything works well we can make it calculate the baseline reading when we press the button. Most of the code needed, we can take from the SATVL.

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I have used quite a few different ATtiny chips in my various projects and I have a few breadboard lying around so I decided to make an ATtiny Programmer Adapter which will suit all ATtiny DIP chips and you can use it with your favourite AVR programmer. You can use a crystal on the XTAL female headers if required.

Download ATtiny_Programmer_Adapter_v1.0 (PCB is untested)

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Following from Part 5 we moved to the ATtiny84 so we could have more pins in order to use SPI and V-USB together and we found that we really shouldn’t be doing anything whilst the ADC is running. In this part we will be upgrading to the ATtiny44A, connecting the SRAM and updating our schematic.

Above is the schematic from the last part.

Change to ATtiny44A and voltage switching circuit

Now it’s time to add in the SRAM however we need to find a way to keep it running at between 2.7-3.6V which means that the current voltage switching circuit we used before won’t work.

The easiest way is to use 2 diodes – one going from 3V to the 5V USB which will allow the ATtiny to be powered by the 3V or 5V, not allow the 5V to recharge the 3V battery and allow the SRAM to always be powered when there is a 3V battery. The next diode goes from the 5V USB to ATtiny just before the other diode, so our D- line will only read as high when the USB is connected and read as high when the battery is connected (used for detecting whether the USB is connected).

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I’ve had a small solar panel now with a voltage of up to 18V (up to 83mA current) for a little while so it’s now time to make a small solar power charger to recharge 12V batteries. Previously I had a solar panel with a voltage of up to 14V which didn’t cut it when the sun was shinning on it for a few minutes; I found the voltage dropped and it wasn’t enough to recharge my 12V batteries.

I chose to use the LM317 regulator as it seems to be a common regulator to use for small current devices. With the LM317 you can adjust the output voltage ranging from 1.2V to 37V by using 2 resistors on the adjust pin.

The primary use of this charger is to keep my 12V batteries topped up. From Wikipedia we find that voltage to keep batteries topped up is called the Continuous-preservation charge which is 13.2V.

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For some time I’ve been meaning to do a new video which covers why using 100% of SRAM can sometimes introduce bugs. I discovered this when I was working on the Nokia 3120 Keypad SMS Sender, the SMS message that I was sending would be cut short and would have weird characters at the end. I loaded up the hex file in AVR Studio 4 and found that the stack was overwriting my variables!

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Element14 has given me another opportunity to review a product from their website, this time I chose the Element14 XL_STAR Development Board which is based on the Freescale MC9S08MM128 MCU that can run at 48MHz and has 128K flash, 12K RAM, 16-bit ADC, 47 I/O pins, SPI, DAC, RTC, to name a few features.

The XL_STAR’s main feature is the interaction between a 3-axis Freescale MMA8451Q accelerometer and an assortment of 48 LEDs around the accelerometer. This allows you to easily prototype ideas for your project ideas that which involve a 3-axis accelerometer.

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Following from Part 4 we tested the ATtiny85 with external SRAM via SPI which worked well however we don’t have enough pins to use SPI and V-USB on the ATtiny85. In this part, we will be upgrading to the ATtiny84.

The ATtiny84 has most features that the ATtiny85 does however I found that it didn’t have the PLL clock to generate the 16.5MHz needed for V-USB when using the internal oscillator. We do have enough pins to use a 16MHz crystal which also works with V-USB.

We use CKSEL as 111 for crystals higher than 8MHz. The factory default for Start-up Times is 14CK + 64ms for slowly rising power, so we’ll use that also for the crystal too.

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Today we’ll be looking at the Netgear DG814 DSL Modem Internet Gateway, it looks to be the first version released which is why it looks so large compared to other routers I have looked at.

Four screws later and we’re in.

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Just thought I’d make a quick post to advise that the Standalone Temperature/Voltage Logger is now available to purchase as a kit here: https://www.insidegadgets.com/projects/standalone-temperaturevoltage-logger

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