Making USBasp Chinese Clones Usable

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.

USB ISP programmer with aluminium 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:

usb 3-1: new low-speed USB device number 3 using ohci-platform
usb 3-1: New USB device found, idVendor=03eb, idProduct=c8b4
usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
usb 3-1: Product: USBHID
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.

Disassembly how-to photo

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.

USBISP programmer, with aluminium case

USPISP PCB rear

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:

Clone difference in schematic view

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.

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Raspberry Pi Zero Wireless

On the 5th birthday of the Raspberry Pi last week, the foundation announced a new addition to the family — the Raspberry Pi Zero W. The W stands for Wireless.

I got my hands on one, from the fine folks at Pimoroni. (And no they didn’t pay me to say this.)

The Pi Zero W board

It has the same specs as the Raspberry Pi Zero, namely the 1GHz single-core CPU and 512 MB of RAM. It still has the two micro USB port — one for power and another for OTG, which means you can get it to behave like USB devices when plugged into a PC. The big difference is that they have added WiFi and Bluetooth capability to this small board by squeezing some space out from between the processor and the power circuitry. The size of the board and the placement of connectors remain the same, even the test points on the back.

I’m excited for anything that has processing power, HDMI connectivity and WiFi.

WiFi + Bluetooth

BCM43438 wireless chipset

The 802.11n WiFi and Bluetooth 4.1 functionality comes from the Broadcom BCM43438 (now known as the Cypress CYW43438). This is the same chipset that was used in the Pi 3. The wireless chipset connects via SDIO, so your network traffic does not have to contend for the USB bus bandwidth.

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Seeedstudio Fusion PCB Review

Fusion PCB is a PCB service from Seeedstudio. They have been offering PCB prototyping service since I made my first board in 2011. It has recently been revamped a little, tweaking prices and options, as well as integrating an online Gerber viewer from EasyEDA. I was invited to give Seeedstudio’s revamped Fusion PCB service a try, and since I had some boards in the pipeline for manufacture, I thought why not?

You can configure various options for the PCB, such as board thickness, copper pour and surface finish. You can also make flex PCBs or aluminium for better heat sinking, as opposed to regular FR4. These options will of course come at a price. However, you can select various colours for your PCB at no additional cost.

The Boards

I ordered 2 sets of boards in total. I’ve decided to opt for an ENIG finish for the TIL311 display boards, just because it looks nicer in gold. The boards are manufactured with black solder mask, making the gold pads stand out better.

I’ll describe the display board in a separate post after I’ve assembled it. For now, here’s what 4 of the boards look like, component side up:

TIL311 display PCBs

Like most PCB prototyping services, they track your order by printing some kind of order identifier onto each PCB. Usually they try to put this identifier underneath a component like an IC so it gets hidden when the board is fully populated, but sometimes they put it somewhere prominent, like under your product name. On this board, the identifier sits under IC4 but for the other board, it was under the product name.

The PCBs arrived in a shrink-wrapped bubbly packaging to protect the boards. There was also a desiccant thrown in for one set of the boards to keep it dry.

PCBs arrived in bubbly shrink-wrap

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Raspberry Pi Zero as Multiple USB Gadgets

In case you haven’t heard, the Raspberry Pi Zero is the smallest, most low-cost device in the Raspberry Pi family, but it’s also the hardest to find. It has two Micro-B USB ports, one for power and another functions as a dual-role USB OTG port.

Raspberry Pi Zero, back side

One of the more interesting uses for the Raspberry Pi Zero is to get it to behave as a USB device, just like your USB flash drive, for example.

There have been several guides written already, such as the Adafruit one, but most of them were based on the old kernel gadget drivers, like g_serial and g_ether. It still works, but not as flexible and likely to be deprecated in future.

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Retro LED Displays

When I saw this post on Hackaday, I thought the display looks cool. Even the people who commented on the post thought so too. This board that you see in the post monitors the bus for the Z80 in the RC2014 retro Z80 computer kit.

After some searching and the wisdom of the Hackaday crowd, I bought a few of them from eBay. It turns out that these displays are no longer being manufactured anymore. These used to be made by Texas Instruments, the TIL311 or DIS1417.

TIL311 / DIS1417 Displays

I like how the display looks like a pseudo LED matrix, forming a 7-segment display. They could have made the edges totally flat, just like a 7-segment display, but they chose to round the corners of certain digits and letters, like 0, 2, 8, A and others.

TIL311 font map

Each display has a built-in chip at the bottom of the digit, which you can see under bright lighting in close-up photos. The chip handles the latching and display logic, and contains a constant-current driver for all the LEDs to output a single hex digit (0-9, A-F). This was handy for old-school logic systems (like the Z80) because each display handles 4 bits, exactly a single hexadecimal digit. You could also interface this display easily without a microcontroller, as opposed to a display that that speaks I2C.

From the date code in the photos, you can that these displays were made in Korea in 1998. The pins look like they are made of gold, or gold-plated.

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