teardown on irq5 test

ONV PD3401G PoE Splitter Teardown & Review

Tue, 02 Apr 2019 11:59:00 +0000

Continuing my PoE series, I bought the ONV PD3401G, an active PoE splitter that is capable of extracting up to 60W (24V @ 2.5A) from the PSE. It is housed in a small aluminum extruded case that can be DIN rail mounted. This splitter is comparatively low-cost, about US$35, and more importantly, is capable of passing through Gigabit.

ONV seems to be quite a reputable company, so I believe their products shouldn’t be too badly designed. This unit can also be easily purchased on Aliexpress without having to go through some obscure distributor.

Internally it uses the LT4275A (marking LTGBT) for PD interfacing. The A variant of this chip supports up to 90W of power. On the power supply side, it uses a NCP1034 synchronous buck converter. The NCP1034 is capable of handling up to 100V, which is more than sufficient for PoE.

Looking inside, the in/out Ethernet ports are connected via a transformer, in order extract power from the center taps of each pair. We can see that the PCB traces for the input port pairs are thicker to carry the higher currents. Large beefy diodes form rectifier bridges for the data pairs.

Surrounding the input port on the underside, there are a lot of unpopulated components; those were supposed to offer input protection, probably using some TVS of some kind. these are marked RD1 ~ RD8, one for each Ethernet wire.

Making USBasp Chinese Clones Usable

Tue, 25 Jul 2017 00:06:00 +0000

I don’t have any dedicated programmers. I have been programming Atmel chips using the USB-to-serial bitbang method.

Recently, I thought I’d get one because doing a re-programming cycle is taking quite a bit of time (a disadvantage of serial port bitbanging).

A popular one on Aliexpress seems to be this “USB ISP” one, so I bought one. I chose this one because it has a nice aluminium case, and a pinout diagram imprinted on the case, which is handy. After having so many one-off projects with bare PCBs collecting dust, I now appreciate the importance of having projects in their own box or case.

While it has “USBasp” in the item name, it turns out that this was not a USBasp device, and getting it to work like one takes some effort.

It identifies itself as a zhifengsoft HID device when I plug it into Linux:

[705621.968025] usb 3-1: new low-speed USB device number 3 using ohci-platform
[705622.199065] usb 3-1: New USB device found, idVendor=03eb, idProduct=c8b4
[705622.205939] usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[705622.213194] usb 3-1: Product: USBHID
[705622.216876] usb 3-1: Manufacturer: zhifengsoft

avrdude does not recognize the device, even after creating an entry with the corresponding vendor/product ID. This particular device was designed to work with their Windows-based UI called ProgISP and will not work with avrdude.

And apparently you can’t just take the USBasp firmware and flash it into this device, because the circuit is somewhat different.

After some research based on the PCB markings, I found these sites that talk about them:

Disassembly

Disassembling the device is simple. While grabbing the side of the case, firmly push the USB connector inwards and the board should slide out the other end. You can then gently pull the board out by the IDC connector.

The programmer seems to be based off of the popular USBasp programmer, but modified somewhat (to what end I’m not sure). It lacks some features offered by other USBasp programmers, like the ability to control the target’s clock, or to use 3.3V for certain targets. But at $2 with a nice aluminium case, what more can you ask for?

It’s powered by an ATmega88 (I read that older versions were based on ATmega8). The markings on the board indicate that this is a MX-USBISP-V4.00. You can ignore tHe date because it was never updated; the older V3.02 also has the same date. While the GreenPhotons blog was talking about V3.00, I have verified that this version suffers from the same issue.

Note that there are provisions on the PCB to add a voltage regulator, and the PCB link marked “C” can be cut to separate USB power from the rest of the system. Link “D” can be cut if you wish to disable target power. However, none of these options were used.

The crucial difference with this clone is that the USB D- pin is additionally connected to PD3, shown here highlighted in blue:

However, in the USBasp’s main() function, PORTD’s data direction register was initialized like so:

 /* all outputs except PD2 = INT0 */
 DDRD = ~(1 << 2);

This causes the USB D- line to be actively driven from PD3, thereby impeding communication to/from the USB host.

The rest of this post will talk about (1) correcting this problem in USBasp, and (2) uploading the firmware into your zhifengsoft programmer.

Paper Shredder Repair

Mon, 06 Apr 2015 12:50:00 +0000

Now is probably a good time to mention that I have a paper shredder. When I was shopping for a shredder, the basic requirement is that it must be relatively “secure”. Straight cut shredders (that produce long straight strips) are definitely not secure.

Ultimately I settled on the CARL DS-3000 personal paper shredder. The DS-3000 is a cross-cut shredder which produces “particles” no larger than 2mm x 4.5mm and this meets DIN security level 4. These days, the NSA mandates 1mm x 5mm “particles” for classified documents.

At this point, it’s probably helpful to show you what my shredder bin looks like:

From the particles, you can make out various truncated words such as “A/C”, “exp” and the number “5”, but it’s almost impossible to reconstruct any bank balances or personal information from it.

This particular model was the right balance between my budget and the level of security. Plus, the shredder is compact enough to sit on your desk. I bought it in 2009 and I use it every couple of months when I have accumulated enough material that needs to be destroyed.

I was in the middle of shredding papers when it suddenly stopped working. Now the shredder does not respond when I stick paper into its slot. The LED indicator looks dimmer than usual when it is turned on.

But I’m not ready to give up on it just yet…

CY-20 Cheap Flash Teardown

Mon, 10 Jun 2013 01:04:00 +0000

Following up on my DIY slave flash project, I thought I’d get something more powerful than that tiny Xenon bulb. I bought the cheapest flash on DX.com - the CY-20. It has a considerably large bulb and as a plus, it has what looks like a tiny window on the front for automatic output control. The main reason for getting this was the 2.5mm jack on the back of the flash that allows it to be externally triggered.

Opening it was easy. Remove the 4 screws that secure the hotshoe mount and go round the casing to release the retaining clips. Surprise surprise, take a look at the sensing window.

Apple's Lightning Digital AV Adapter

Mon, 11 Mar 2013 22:39:00 +0000

Recently, Panic noticed the odd output resolution and MPEG-like artifacts with the new Lightning digital AV adapter and decided to take a hacksaw to it. They found an ARM processor inside. image credit: Panic blog Shortly after, they received an anonymous comment that explains it all: The reason why this adapter exists is because Lightning is simply not capable of streaming a “raw” HDMI signal across the cable. Lightning is a serial bus.

How Electret Microphones Work

Thu, 07 Apr 2011 18:39:00 +0000

There’s a really nice article on Open Music Labs that describe the inner workings of the ubiquitous electret microphone.

Dissecting the SoundGraph iMON MM

Sat, 22 Jan 2011 17:01:00 +0000

Correction: The device is actually an iMON Multi-Median (MM), which includes an IR receiver and a remote control. My friend recently passed me a brand new unopened SoundGraph iMON IR receiver device. Here’s how it looks like: As you can see from the box, it supports up till Windows XP. If you’re thinking how the terms “Windows XP” and “brand new unopened” go together, it’s because he’s kept it for 4 years.