Repairing a 1960s mainframe: Fixing the IBM 1401’s core memory and power supply


Ken Shirriff wrote a great article describing the repair process of  the vintage IBM 1401 mainframe computer:

The problem started when the machine was powered up at the same time someone shut down the main power, apparently causing some sort of destructive power transient. The computer’s core memory completely stopped working, making the computer unusable. To fix this we had to delve into the depths of the computer’s core memory circuitry and the power supplies.

See the full post on his blog.

Arduino controlled Dual Mono AK4490 DAC (part 2)


An update on Arduino controlled Dual Mono AK4490 DAC project we covered previously:

After I was certain that everything related to the software was working the way it should, I designed a “motherboard” that would take care of the following:

  • Accept the STM32F106 board
  • Accept the 3.5″ TFT
  • Accommodate an 24LC256 EEPROM chip, used to store the DAC’s configurable settings
  • Accommodate two sets of I2C signal isolators and I/O expanders
  • Include headers for the encoder, IR receiver, power relay, non-isolated and isolated I2C communication, unused uC pins, etc

See the full post here, Dimdim’s blog.



Angus Ainslie writes about an open source project a CHIP Pro TNC:

So I finally have a design of the TNC I’ve been working on that I think is ready for release. Initially this started with me wanting a replacement for my mobilinkd and AP510. With feature creep it has turned into much more.
The current board has a VHF radio module, a CHIP Pro computer module running Linux ( NTC calls it gadget OS ) and a Mikrobus slot. I’m currently using the Mikrobus for a GPS module but there are lots of variants.

See the full post on his blog.

BML USB 3.0 FPGA interface over PMOD


An open-source-hardware USB 3.0 to FPGA PMOD interface design from Black Mesa Labs:

Black Mesa Labs is presenting an open-source-hardware USB 3.0 to FPGA PMOD interface design.  First off, please lower your expectations. USB 3.0 physical layer is capable of 5 Gbps, or 640 MBytes/Sec. This project can’t provide that to your FPGA over 2 PMOD connectors – not even close. It does substantially improve PC to FPGA bandwidth however, 30x for Writes and 100x for Reads compared to a standard FTDI cable based on the FT232 ( ala RS232 like UART interface at 921,600 baud ). A standard FTDI cable is $20 and the FT600 chip is less than $10, so BML deemed it a project worth pursuing.

More details at Black Mesa Labs homepage.

Via the contact form.

App note: Power source ON/OFF characteristics for linear regulator


A good read app note from ROHM on linear regulator On and Off characteristic. Link here (PDF)

When a linear regulator IC is turned ON, the electric charge is stored in the output capacitor and the output voltage increases up to the specified value. At this time, an inrush current flows from the input to output of the IC. The output voltage drops when the input power source is disconnected. This application note explains the series of operations when the power source is turned ON/OFF.

Small USB to PTT/CW adapter


Mare writes, “In this post, I will first introduce some of the basic technical background of the control of the transmit signal (PTT) and other signals (eg CW or linear activation). The second part will describe the  interface development and the final product.”

More details at Mare & Gal Electronics blog.

Sense energy monitor teardown – sampling in MHz

Sense Energy monitor teardown

Tisham Dhar did a teardown of a Sense Energy monitor:

Recently I obtained a Sense Energy monitor via US from Margaret of BitKnitting. She is doing a very interesting neighbourhood energy efficiency project. As usual I could not contain my curiosity and opened it up to have a look. I will start off with an analogy – the closest bit of open-source kit that I have to do half the amount of analog functions as the Sense is the PRUDAQ on the BeagleBone wifi

More details on his blog.

SIM800 GSM module

Today I received from  Banggood a GSM module based on the SIM800 chip by SIMCom. I’m going to use this module in a future Arduino project that will allow me to remotely control devices. In this article I’ll show you how to test the module.

The SIM800 is a quad-band (850/900/1800/1900MHz) chip and allows to trasmit/receive voice, SMS and data (using the GPRS network).

The small module (about 3x4cm) has the SIM800 chip and most of the components on one side, while on the other side you can find the sim card connector:

gsm-005 gsm-004

I chose to buy the module with an external antenna… in addition to the module you therefore receive the antenna and a short (about 20cm) cable to connect it:


The module is powered with 5V, offers a serial interface and you can control it using AT commands.

It is very important to connect the module to a power supply able to provide up to 2A, otherwise you may face problems on the stability of the GSM connection.

To verify if the module works you can therefore connect it to your PC using a simple USB – serial converter and send the correct AT commands as the manual explains. Be careful to invert the TX and RX pins: the TX pin of your adapter must be connected to the RX pin of the GSM module and viceversa:

gsm-008 gsm-007

The simplest test is to send and receive an SMS. For simplicity first configure the text mode (=1) with the command AT+CMGF=1. The module will answer with the command you send (without the starting AT) followed by OK.

Now you can specify the recipient of the message with the command AT+CMGS=”number. After having sent the “carriage return” character, the module will send the prompt, after which you can type the text of the message. End the message with the character 0x1A (CTRL-Z); the module will answer with the command you sent followed by the number of characters in the message (26):


When a new SMS is received, the module sends the +CMTI message. You can read the messages with the AT+CMGL command and you can also specify a filter (for example REC UNREAD, that is all the messages received but not read yet):


The filters available are listed in the manual:


After having verified that the module works, you can now realize a more complex project, for example interfacing it with your Arduino…