Tektronix TDS 520 repair

Update: Added a link the Debug Interface schematics (pdf)

The Tektronix TDS 520 is a digitizing oscilloscope from the early 90s. It offers 500 MHz analog bandwidth, 500 MS/s sampling rate, 2 full-featured channels and 2 auxiliary channels with a limited vertical sensivity. Although being at age nowadays, this oscilloscope has perfect properties for a prominent place in the shack at home.

My TDS 520 was saved from the scrapheap.

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PiVPN suddenly stops accepting client connections

PiVPN for Raspberry Pi is a wonderful and easy OpenVPN setup tool. I use it a lot with various devices to access my home network. But it suddenly stopped accepting connection from those various devices. This is how I solved the issue…

This is what /var/log/openvpn.log showed:

Wed Jan 23 20:09:47 2019 VERIFY ERROR: depth=0, error=CRL has expired: CN=tim
Wed Jan 23 20:09:47 2019 OpenSSL: error:14089086:SSL routines:ssl3_get_client_certificate:certificate verify failed
Wed Jan 23 20:09:47 2019 TLS_ERROR: BIO read tls_read_plaintext error
Wed Jan 23 20:09:47 2019 TLS Error: TLS object -> incoming plaintext read error
Wed Jan 23 20:09:47 2019 TLS Error: TLS handshake failed

So… The certificate has expired.

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Interface a rotary encoder with Atmel AVR (interrupt style)

When I wanted to gently interface an incremental rotary encoder with an 8-bit Atmel AVR microcontroller, I couldn’t find a nice example. That’s why I wrote this little text. Many other howtos, manuals and descriptions are fuzzy, incomplete or too complicated to do the (easy) job.

This article describes three things: the hardware (just the minimal hardware) and two pieces of code. The first is just a simple interrupt based program and the other uses timers to make bigger steps when you turn faster.

I use Atmel AVR studio as IDE and the Through hole USBprog to program the microcontroller.

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