Blog - All Comments

RE: Simple DCR: Assembling a 7 MHz (40m) Direct Conversion Radio Receiver – Part 1

rsjawale24 — Sat, 25 Jul 2026 12:34:38 GMT

As a kid, I always wanted build a receiver myself, but I could never build one as it was difficult to find toroidal cores locally and then wind the inductors. I used to look for circuits that do not use them.

RE: Discrete difference amplifier - AC analysis: gain and bandwidth

Jan Cumps — Mon, 20 Jul 2026 12:51:21 GMT

IN1
out
Q4 collector

conditions:

V+: 9V
IN1: sinus 1 kHz, 100 mV_rms
IN2: ground

RE: Discrete difference amplifier - DC analysis

Jan Cumps — Sat, 18 Jul 2026 08:26:57 GMT

Explanation from CAN education. There are a few differences in the circuit but the overall explanation holds:

- slightly different active load / current mirror (connection of the Q2 and Q3 basis, R13

- different current source topography. Assume 2.2 mA in our circuit

[View:https://www.youtube.com/watch?v=dGHeuBZ-6eQ:640:360]

RE: Discrete difference amplifier - AC analysis: gain and bandwidth

Jan Cumps — Fri, 17 Jul 2026 09:10:44 GMT

[mention:b0bc65b9ecdc4307bd967592f00e340a:e9ed411860ed4f2ba0265705b8793d05] , the current source in the tail of the differential amp (orange area below):

what was your inspiration to design that sub-circuit that way?

RE: Discrete difference amplifier - AC analysis: gain and bandwidth

Jan Cumps — Thu, 16 Jul 2026 09:57:30 GMT

For the next blog, I plan to

show some internal signals
test how the circuit behaves when there is an identical signal on both inputs (desired/theoretical result: no output signal)
go into the design, maybe based on Art of Electronics:

RE: Discrete difference amplifier - AC analysis: gain and bandwidth

shabaz — Wed, 15 Jul 2026 11:39:00 GMT

Hi Jan,

Very useful information! I had not got the stripboard prototype working too well (I probably made a soldering or component error somewhere) so it is great to see these real measurements with the PCB.

RE: Discrete difference amplifier - AC analysis: gain and bandwidth

DAB — Tue, 14 Jul 2026 20:45:16 GMT

Very cool Jan.

RE: DMX Explained; DMX512 and RS-485 Protocol Detail for Lighting Applications

shabaz — Sun, 12 Jul 2026 22:42:36 GMT

This article is almost nine years old, and unfortunately a lot of the images had lost resolution during a website upgrade. I've re-uploaded better quality images from that time (they would be a lot higher res if I were to redo it now). But at least the 'scope traces are finally readable again.

RE: Discrete difference amplifier - DC analysis

Jan Cumps — Sun, 05 Jul 2026 10:13:29 GMT

first signal measurements.

I used a 100 mVpp, 1 kHz sinus. Output loaded with a 27K resistor.

signal at in1, in2 to ground
signal at in2, in1 to ground
same signal at both

the amp does what it needs to do. Amplifies differences, reject the same signal

AI says the gain is 7.96 dB.

> what is the gain in dB if I input 100 mV peak-to-peak and I get 250 mV peak-to-peak out?

RE: Discrete difference amplifier - DC analysis

DAB — Sat, 04 Jul 2026 20:52:47 GMT

Very interesting.

Well done Jan.

RE: Discrete difference amplifier - DC analysis

shabaz — Sat, 04 Jul 2026 15:41:19 GMT

Nice setup! Love that triple-output power supply, it looks like a very useful beast.

If anyone is interested in simulating things with KiCad, this is a suitable example project for that I think, and more useful now that people can see the values in reality too for comparison.

The screenshot shows how to get to the simulator in KiCad:

And then one button-click to run the simulation, and the values for each node in the circuit will be displayed directly on the schematic:

RE: GitHub for Professional Beginners: From First Repository to First Release

shabaz — Tue, 16 Jun 2026 17:59:39 GMT

Even if I don't have a proper strategy, and am just working on a small personal project, bits of the process can be followed minus the development branch. For example, I have a small project in my own repository, I know no-one else is working on it, and I only have a main branch. This would be the situation at the start of a lot of simple projects I imagine.

On the PC, I had done a git clone to obtain the repo contents, and directly made and tested some code changes which have essentially ended up implementing a new feature. How can I get those changes into the repository?

I decided to create a feature branch after the fact that I had already worked on the feature, and merge that into main. You'd never do this for a real project where you'd want the ability to test multiple features before putting them into main; for that, you'd need the development branch to test an entire combination of new features thoroughly before merging into main. But this is my small project, I'm the only coder and tester, and I only want to merge one feature that I have tested (both feature and integration, since there are no other features to be integrated), and I'm not creating releases (so far!).

I did this:

git switch -c feature-acmeas  # create and switch to a branch called feature-acmeas

git add .  # prepare/stage the files for commit

git commit -m "Add AC measurement functionality"

git push -u origin feature-acmeas  # publish your feature branch to the remote (origin)

Then, I went to the GitHub repo web page, and clicked on Pull request, and created that as described in the blog post, requesting a merge into main, from the feature branch. I clicked through to perform the merge.

Finally, to delete the feature branch:

git checkout main  # get away from the branch that is to be deleted

git pull  # update the view with the latest from the origin

git branch -d feature-acmeas  # delete the local feature branch

git push origin --delete feature-acmeas  # delete the branch at the origin

All done!

RE: GitHub for Professional Beginners: From First Repository to First Release

balajivan1995 — Mon, 08 Jun 2026 16:47:17 GMT

Nice write up. But something seem to be missing and it took me a while to realise the part where git asks for password to push local commits to remote branch is missing.

RE: GitHub for Professional Beginners: From First Repository to First Release

DAB — Sun, 07 Jun 2026 19:58:56 GMT

Very good post.

RE: GitHub for Professional Beginners: From First Repository to First Release

shabaz — Sun, 07 Jun 2026 17:11:59 GMT

Just added the following diagram to help follow things.

I hope it's correct, but if anyone spots any error, please let me know!