2019. április 29., hétfő

GP-IB 2.

The boards are arrived a few days ago.

I made a few but not fatal mistakes with the board, and left a few room for improvement also:

  • Cosmetic: the board designation is on a wrong layer
  • Order: only ordered 5 boards (I think 10 would be the same price)
  • Room for improvement: the board uses female IEEE-488 connector. With a few modifications it can be used with male connector also
  • Room for improvement: proper mounting holes
  • Room for improvement: isolated (it needs some investigation if it required)
  • Room for improvement: buffering + bus protection

During the weekend I built and tried it out

The CH340G USB Serial interface was working for the first trial.
The ISP was working for the first trial - uploaded the Arduino bootloader.
The software built and uploaded without problem.
The communication via the terminal emulator with the firmware worked without problem.

Now go and get an instrument to try it out.
As I previously mentioned, I built this interface to communicate with my HP Audio Analyzer. This equipment is not a cheap one if we are talking about a home lab, so I didn't want to sacrifice for the first test. I have several HP 3478A multimeters on hand. Two of it even not part of my lab setup.
So, I tried to communicate with it.
Half success:
When I send a command to the instrument, it does nothing.
When I send a ++read command it responds with the value actually on the instrument's screen.
I was thinking, what could be the problem.
The original design pull down the GPIB PIN 17 (REN - Remote Enable) to the ground. In my build it is connected to one of the MCU pins, to be able to further develop the project. Naturally the original firmware doesn't handle this. So I added a few lines of code to pull the REN pin to low, and the system started to work immediately.

The first goal of this project successfully achieved. The design files of the board can be find here:

As the owners license of the source code doesn't allow modifications, without consent, I'm not publishing the either the original source code or my modifications. I'm intend to contact the author to discuss about the license.

Last but not least:
Many thanks for Emanuele Girlando for his great work.

2019. április 27., szombat

Home references - Resistance

It is a long standing dept for myself.
I bought a few Vishay S Series precision foil resistors to act as resistance standard for my home lab.
I was thinking what would be the best enclosure for them, and in the long thinking process finally the resistance standard process is shelved.
A few weeks ago finally I ordered small aluminum boxes and binding posts for this.
The boxes, binding posts arrived, so I put everything together. As this is a quite simple thing, so not too much to talk about. Here are the pictures:

Measured (the 4 wire mode here is unavoidable):

All of the four values (100 ohm, 1K, 10K, 100K) boxed, labeled:

After finished the labeling, I was thinking about, how can I protect the paper labels from the usual dust in the lab. Here come the advantage of being father of three school age kids. The transparent adhesive foil we use to protect the textbooks are perfect here (and I've tons on stock).

2019. április 6., szombat


In the past years I collected a good amount of test equipment. I mostly using them as standalone instruments (except my PC based oscilloscope).
I recently bought this nice Audio Analyzer on the eBay

I realized, that most of the measurements I bought this unit for are require PC connection.
Even I found a software for it:

As most of a bit aging test equipment only have HP-IB/GP-IB/IEEE-488 interface for the PC connection. No USB, Ethernet, whatever today's fancy stuff.
Buying a decent GP-IB interface is not so easy/cheap today. Yes, I found a few on various sources, but was not happy with any of it. So I decided to build my own.
Found this project on the internet:
Based on this, I designed a board:

Ordered it, so I'm waiting to arrive, to continue the project.