So I was making a modification to the Standalone Temperature Logger (SATL) to make it log voltage instead of temperature and happen to discover an issue with the Brown-out Detector which is set to 2.7V. Download the SATL v2.1 or visit the SATL project page.
It turns out that I had a 3V coin cell which was a bit discharged as it was sitting at 2.95 volts and when I connected it to the circuit it would drop to 2.7 volts and draw about 0.5mA of current which was very odd. At 2.95 volts I thought it should still have some life left. After trying to program very simple programs to the ATtiny85 like a blinking LED, making it sleep right away, etc I had no success. Eventually I reset the fuse bits and it all started working well again which lead me to discovering that BOD was the issue.
I tried adding 0.1uF, 4.7uF and 470uF capacitors which sometimes worked but it wasn’t reliable. I’m now recommending that BOD be disabled for the SATL unless you know the 3V coin cell is brand new or near new condition. The BOD issue brought my attention to other places within the SATL that could be improved upon.
Increase the button pull down resistor
Connected to the button we have a standard 10k pull down resistor and each time the button is pressed or held 0.3mA is consumed, seems sort of wasteful.
In this video I show how you can use a 32KHz watch crystal on an ATtiny85 for precise timing.
We use the timers overflow to indicate when 1 second has passed which wakes up the ATtiny85 and turns an LED on or off and then goes back to sleep (which when in sleep mode with the LED off, it consumes about 60-70uA of current).
This can be used for applications such as clocks, data loggers, etc. If you are looking to minimise the current consumption when sleeping you’ll need to find a AVR with an independent timer clock like the ATmega328 so you can put the AVR on power-down whilst the timer is still running.
Today we’ll be tearing down the Netgear ProSecure Unified Treat Management UTM10; a device that inspects network traffic entering your network.
A few screws later and we’re in. We can see on the left is a small power supply, below that is a small board that has a USB connector. We’ve got 2 chips with heatsinks, one which looks like a piece of stone. There is also an Apacer 2GB CF card which I’m guessing is where either the firmware might live or where logs, etc will be kept.
Just another quick one, I’ll be taking a look at a HP ML350 G6 Server’s hot plug power supply with Part No 499250-001 (Spare Part No 511777-001).
It’s quite a small unit and as you can see it doesn’t have the usual power supply connectors.
The usual power supply components are present.
There does seem to be some temperature monitoring going on; which is something that I guess should be expected if you’re using a power supply on a server, you’d want it to have all the features.
Quite a lot of components on the board than what you’d normally find. That’s all for this quick teardown.
It’s that time again… time to take something apart :). This time it’s the D-Link DE-824TP 10BASE-T Ethernet Hub which I bought second hand back in 2003. Yes this one’s a hub, not a switch!
Just going to be a quick one.
We can see the power supply at the top left. The main board has 24x Ethernet filter modules for each port and 3 microcontrollers each handling 8 ports. There’s a BNC and AUX connectors at the back.
Just a close up of the power supply, to me it looks nicely laid out. What’s a bit odd is how the diodes are directly touching the board, they are a few centimetres above it.
Hehe, I just had to take this picture. I should have something made a bit more recently for my next teardown.
The Standalone Temperature Logger has now been updated to v2.0 with the PCB, schematic, guide and source all available for download.
I kind of took a little break and came back to figure out the PCB, once it was done all that was left was to try it out and create the new documentation for it. Since I’m using 2 SMD Mosfets I thought that soldering them would be really difficult but it turned out to be easier than I expected. Testing went well and am quite happy with how it turned out.
Last week we built an automatic voltage switching circuit and now it’s time to apply this circuit to the Standalone Temperature Logger (SATL).
Let’s bring up the new schematic for the SATL with the voltage switching circuit. As you can see like last week, we separate the grounds of the voltage sources – the 3V battery and USB. Notice that CRTGND is not the same as GND, CRTGND connects to the mostfet drain/schottky diode.
There is a downside to this circuit which is that there is a voltage drop when running from the USB side due to the diode. The USB voltage can vary between 4.75V to 5.25V and the good news is that our ATtiny85 can run fine at 16.5MHz whilst at 4.0V.
If the USB voltage was really 4.75V, we would just make it to 4.05V but we want the best possible voltage even if it was 4.75V. Instead of using just a standard diode we’ll use a schottky diode which can provide a lower voltage drop of 0.3V instead of the 0.7V from standard diodes.
Today we’ll introduce the N Channel Mosfet and show how we can use it to allow us to switch between voltage sources.
Mosfet explained and example
We can think of a mosfet sort of like a transistor, it has a gate, drain and source compared to the transistor which has base, common and emitter.
With transistors that we want to act as a simple switch it’s all about adjusting the current at the base however with mosfets it’s actually the voltage at the gate that turns them on. Because we don’t lose current when turning the mosfet on, this means that it’s actually more efficient than a transistor.
In datasheets you see it called Vgs and they provide you a minimum voltage that is needed before the mosfet will allow current to flow through the drain and the source.
Today I’ll be showing how we can integrate the Standalone Temperature Logger (SATL) into the V-USB Test program we have. It’s taken me a little while to find my way around V-USB and its kinks.
Schematic
The schematic has been updated to include the USB port. Another change is that when the LED turns on it also turns on the thermistor, before we used to do this with the dataPin.
Cleaning up the V-USB code
The first thing I’ve done is copy over our setup.c file from the SATL WinAVR to our project and then move everything related to V-USB setup or procedures (except the sending of keys) to our setup.c file which now leaves us with just two functions in main.c (evaluateADC and main).
Next I would like to cut down on the main’s USB setup code, lets make a new function called startUSB() and place all the code below in it.
In this demo we show how we can change the ATtiny85 clock speed on the fly by modifying the prescaler. We note that using _delay_ms() is subject to the F_CPU and if we double the MHz we need to double _delay_ms() in order for the timing to be correct. Changing the clock speed on the fly may be useful for power saving applications where there might be brief moments to increase the clock speed, e.g. communicating with devices like USB.
AdvanceVGA – Play your GBA on the big screen! Swap out the LCD for our board, solder some wires, connect 5V USB and VGA and you’re ready to go.
GBxCart RW allows you to backup GB/GBC/GBA ROMs, save or restore game saves and re-write supported flash carts. Mini RW option available for GB/GBC only.
Wireless Gameboy Controller – Use your Gameboy, mGB, GBC, GBA, GBA SP, GB Micro, NDS and NDS Lite as a wireless controller on Windows, Linux, Raspberry Pi, etc, and on your NES, SNES, N64, Gamecube and Wii.
