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Today we’ll be taking a look at a Generic 8 Port USB/PS2 KVM Switch which has 8 ports which you can switch to with 2x USB/PS2 inputs and a monitor output. There are no markings on the vendor on the outside of the box.

After a few screws we’re in.


(Picture might look a little distorted due to Pano stitching)

Once inside, we can see the PCB doesn’t use up all of the space available. They are using one chip 8 times (as you might expect), have a little bit of logic (2x 74HC13 and 2x 74HC14), there’s a main chip and a chip for each USB port. There is a 6x 2 pin header for the main chip, the front panel buttons/LEDs connects via a 34 pin connector and there is another 34 pin connector spare with some unpopulated components nearby, wonder what other functionality they could have added. PCB date is 30th week, 2004.

The input voltage to the KVM is 9V so we have an ST L7805 bringing it down to 5V with a decent pad for heat dissipation plus an AMS1117 LDO.

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We had a working touch lamp and then all of a sudden it wouldn’t work anymore, it’s happened to a similar lamp, these lamps are probably 10 years+ old, it’s a Mirabella TL007.

After a quick inspection, the circuit board didn’t smell or look too good. We could try to find the fault and repair the board but I thought it might be more interesting to make our own touch lamp with an ATtiny and just re-use the existing lamp base.

I won’t be wiring it up to the mains, instead since I have an alarm clock already running at 5V (with an 3.3V LDO), I can just wire up directly to the 5V source. The LED will just be one of those 1/2W LEDs you can pick up off Ebay for $1-2 so we’ll just need some dropper resistors or if you wanted to, you could make or buy a constant current driver.

For the touch sensing, you can buy a chip to do that (or it could be integrated already to an MCU you choose) or do it by hand, of course I went with the by hand method as I’ll be using an ATtiny13A. Once touch is detected, we’ll just turn on a mosfet to power on the LED.

To start off, we can use the ADC on a pin to look for any voltage fluctuation but we can’t just leave the pin floating, the pull down resistor needs to be high enough that the pin won’t float, can’t be too low or it won’t detect when we touch it, for me that ended up being 4.7M ohms.

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I’ve recently started to replay some Gameboy games on my Gameboy Colour, I picked up a Gameboy Advance and eventually got around to doing the AGS101 mod to it which makes it look really nice. Eventually I got to the point where I would have to keep recharging the AA batteries I was using as they weren’t lasting as long and the weight of the 2x AA 2000mAh rechargeable batteries made the GBA feel a bit heavy.

I saw a post where someone fitted a 2000mAh LiPo battery to their GBA, they had do to some modifications to the GBA battery compartment to fit it all. By using a LiPo battery instead of the AA’s, it would save us about 20 grams, while not a lot, ever gram does count and you can tell the difference plus since the LiPo has a higher voltage, it has a higher energy density, so it should give us longer play time than the AA’s. So I decided I would do the same mod and I might make a little voltage regulator and charging board to go along with it.

We can’t just directly hook up the LiPo battery to the GBA, you have to step it down to around 3V. You could go higher but I chose not to as who knows what that might affect seeing as the the GBA has a DC-DC boost converter on board stepping it up to 3.3V/5V.

A DC-DC buck converter could do the job to reduce it to 3V and so could an LDO but from my experiences, both of these options seemed to have quite a high quiescent current (usually around 1mA), we would waste power even when the GBA was powered off. One way around this would be to keep the device in shutdown but then how would you detect if the GBA was powered on?


GBA Reg & Charge v1.1
(sneak peak)

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Just a quick one today, we’ll be taking a look at Hahnel UniPal Universal Battery Charger which can charge AA/AAA/Li-Ion and also outputs 5V for USB. This charge allows the user to change the Li-Ion battery contacts via the blue gears.

3 screws later and we’re in.

There isn’t too much going on, just a single chip solution and there are no marking on it. You can see how the blue gears and the wires going to the contacts have been heat-shrinked to protect them a bit more.

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Building an ESP8266 PC Power Cycler

I know this sort of project has been done before but nevertheless it’s still an interesting project to try and put your own spin on it. The idea is to have an ESP8266 which can press/hold the power button and might as well have it also read the power LED state, you could also wire up the reset button if you wanted to, it’s a good concept for servers (or PCs) which don’t have a remote management and you need something basic.

(sneak peak of prototype)

One option might be using the 5V standby power which most power supplies provide when the PC is off. Some PCs might have 5V standby available in the BIOS, the keyboard and mouse might stay on, maybe you could find some pins on the mainboard but perhaps some mainboards might not have it? Let’s just avoid it all, I’m thinking I could have the ESP8266 powered off a 3.3V LiFePo4 battery in a small little case which when the PC is on, it will recharge itself via USB, this way we don’t need the PC to be on or have the ESP8266 powered via a mains adapter.

For the circuit, we can sense the power LED, it will have a voltage drop out say 2-3V with the LED but could have 5V if the LED isn’t connected for whatever reason, we’ll just use a NPN to switch 3.3V on or off to our input pin. The power switch we can use an opto-isolator to turn it on or off which can be inline with the power button. We can also integrate the USB LiFePO4 charger into this project to charge the battery.

That’s pretty much all there is to the hardware, now for the software which is where it’s all at. We want to make it as simple as possible to setup without needing any port forwarding on the client’s end, so the design is to have the ESP8266 reach out to a server to fetch a command over HTTPs. We don’t want the ESP8266 to be awake all the time otherwise the battery won’t last long so we’ll utilise the deep sleep function and say wake up once every 5-10 minutes.

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I’ve built a 32KB Gameboy cartridge before to add support for certain flash chips to GBxCart RW but those were wired straight through without the need of an MBC so I thought it might be interesting to jump back into CPLDs by building an 2MB Gameboy cart.

We have a few options when building a Gameboy cart, use 5V Flash chips (which are pretty rare these days) with 5V SRAM chips or go 3.3V Flash/SRAM chips and use level shift transceiver with direction control to interface with the Gameboy’s 5V logic. Because this is my first real cart, I’m going with easier the 5V flash/SRAM chip option for the moment.

(sneak peak of the cart running a game)

The only flash chip I have on hand is the 512KB AT49F040 so I’ll use that at the start and then we’ll transition to the 2MB AM29F016B in a later part once it arrives. For the MBC, I have an Altera EPM3032 CPLD handy so we’ll go with that, it runs off 3.3V so we’ll need an LDO for it and the inputs accept 5V logic.

Initial Planning

 

Let’s get started, firstly we’ll review the MBC5 documentation to determine which addresses the CPLD will need to read for changing ROM banks/RAM banks, etc. The lowest address is 0x0000 – 0x1FFF for RAM enable, the highest bit of that address that’s a 1 is A12 so that’s where we will start. The highest address is 0xBFFF when accessing the RAM, so A15 is where we will end, that makes 4 bits which are needed for listening to incoming MBC requests.

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Today we’ll be taking a look at Plustek OpticSlim M12 Corporate USB Scanner which is a single sheet scanner, powered by USB.

2 screws later and we’re in.

The shell comes apart, we have the small buttons PCB on the top and the scanner and motor on the bottom. A few more screws later and we’ve got to the main PCB.

We have a relatively long PCB that has single chip solution with a motor driver. The scanning element was connected with a flat flex cable. PCB date code is 1st week of 2007 but it’s strange that they have another date code of 2002 on the board, maybe this PCB was part of an older product.

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I’ve playing around with DC-DC step down converters but haven’t really had a need for step-up converters until recently. I have a portable device which requires ~12V 100mA so I’ve been powering it with 4x 3.3V LiFePO4 14500 batteries so it would be nice to reduce the weight a little bit by using a step-up converter knowing that the run-time will decrease.

So I went looking around for some chips and found the Micrel MIC2288 for 90c which supports 2.5V to 10V input, up to 34V output and 1A switch current. A quick look at the datasheet and the BOM looks good and the efficiency chart seems to say it can do at least 100mA at 3.2V so it’s looking good.

So I built it all up, used a 15uH inductor instead of the 10uH they showed. On the output I got 11.8V so all seemed well, put a 1.5K resistor (8mA load) which was fine, then I tried 330 ohm (36mA load) and that’s when I saw the voltage drop to 9V or so on the multimeter, strange plus I heard some sounds coming from the circuit. I started bumping up the voltage from 3.3V and once I hit 5.2V the output seemed to go back to 11.8V. I went back the other way, once I hit 2.3V to 2.8V it started working normally again. No components were getting hot.

I swapped the inductor for a 22uH one, same issue. I was about to measure the voltage across the Schottky diode when I touched the first lead to the SW (point where the inductor and Schottky diode meet) and the sound went away and the voltage went back to 11.8V. The current draw at 3.3V input was 150mA and it stayed the same when touching the SW pin. I swapped out the Schottky diode for a larger one but there was no change and touching the SW pin didn’t work this time.

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Today we’ll be taking a look at D-Link 8 Port Gigabit EasySmart PoE Switch (DGS-1100-08P) which is an 8 port switch with 8x 10/100/1000 ports with POE rated for up to 64 watts.

2 screws later and we’re in.

We’ve got our main chip with a decent heatsink plus 3 other chips. The PCB looks to have some isolation with transformers, optoisolaters between the 48V input / PoE side to everything else.  We have a few logic chips – LVC14A Inverter and 2x 74VHC164 Shift registers. There are 2 headers, one 4-pin one 6-pin near the main chip. On the bottom of the board, we can see they left off the solder mask for slightly better power dissipation on the PoE chips. PCB date code is 27th week of 2013.

All the electrolytic caps seem to be branded KY. No SMD inductors were used which makes the smaller through hole inductors look a bit strange in how they were placed.

We have the 48V coming in, pass a switch rated for 3A then to the DPA422 DC-DC which provides an output through the transformer to lower the voltage for the M3Tek IT7802 DC-DC which outputs 5V. The 48V input also feeds directly through an choke to the PoE chips.

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Building a Simple LiFePO4 USB Charger

Since I’m starting to use more LiFePO4 14500 batteries I thought it would be a good idea to build a simple USB charger for them instead of having to charge 2 at a time on the xxx battery charger. The most simplest way would be to stick it on a CV/CC power supply or another way is to stick it on a CV power supply set to 3.6V with say a 1 ohm resistor and wait for it to reach 3.6V, not the quickest to charge but it works.

My first design was to use a voltage reference such as a TL1431M (or a resistor & zener diode) set to 3.3V with a decent op-amp like the MCP6242 with hysteresis threshold set to 3.2V – 3.6V and an PNP transistor to switch the 5V through say a 10-20 ohm resistor to the battery. This would only charge the battery if it was under 3.2V, stop at 3.6V and won’t start charging again until the battery dropped back to 3.2V which it shouldn’t.

It works one problem arises when you unplug the USB side and leave the battery in, it would start discharging a few mA due to being connected to the op-amps output but it’s not like that would really ever happen. But let’s put in an MCU, say an ATtiny13A to sort it out. I have plans to make a device in the future run off the LiFePO4 battery and recharge itself when the USB cable is connected if it matches the threshold voltages as before.

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