insideGadgets

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: http://www.insidegadgets.com/projects/standalone-temperaturevoltage-logger

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Following from Part 3 we tested logging the op-amp’s output, storing the results in the ATtiny’s SRAM and transferring it to the PC. Now we’ll use external SRAM instead of using the ATtiny’s SRAM.

I’m using a Microchip 23K640 SRAM which has a voltage range of 2.7-3.6V. It looks like with SRAM there aren’t many around that can do 2.7-5.5V, this means we won’t be able to power the SRAM from the USB directly when transferring data, we’ll need to use a regulator and level shifters.

Before we integrate the external SRAM to our current schematic, we need to take a look at how to access it, it uses the SPI protocol. SPI is as simple as I2C except that instead of accessing a device by address, you pull the chip select line on the device low and instead of 2 wires you need 3 wires (plus one from chip select). Potentially you could have a lot of SPI devices on the same bus, you would just need a chip select line for each of them.

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