Evan K7FOS

I'm a software engineer in the adtech industry!

In my free time I like to make stuff. I also like to make stuff that makes other stuff.

[Evan K7FOS @k7fos]

I finished some updates to my RF mixer circuit (Gilbert Cell topology), and have been testing it out! 7.1dB drop between the fundamental and mixed frequency, and a max signal-to-noise of 58dB! Not amazing, but it will work fine for my plans.

[Evan K7FOS @k7fos]

@freddyphysh @fibersphere I wish they'd at least say what is going on, and perhaps an ETA.

[Evan K7FOS @k7fos]

My first successful attempt at solar photography! And all from the convenience of my window!

[Evan K7FOS @k7fos]

Lots of breadboarding lately! Fun audio projects to boost my op-amp skills.

[Evan K7FOS @k7fos]

Somehow one of my dorkier purchases over the last year -- a 4-foot-wide Pickett slide rule! It was originally used as a teaching aid during the era of slide rules. I am unreasonably happy with finding this one!

[Evan K7FOS @k7fos]

AGC circuit I've been working on.

(1) Voltage divider w/ an n-channel MOSFET as a variable resistor
(2) Buffer amplifier (output green)
(3) Peak Detector (output red)
(4) Comparator of peak voltage vs reference voltage. Provides feedback to the MOSFET.

https://t.co/jh9ysIdOVc

[Evan K7FOS @k7fos]

Here's what the circuitry looks like, roughly. I built this up when I was learning about double-balanced mixers. https://t.co/bu4xTMlOYy

[Evan K7FOS @k7fos]

I finished some updates to my RF mixer circuit (Gilbert Cell topology), and have been testing it out! 7.1dB drop between the fundamental and mixed frequency, and a max signal-to-noise of 58dB! Not amazing, but it will work fine for my plans.

[Evan K7FOS @k7fos]

New crystal oscillator circuit board! I designed this one to be able to be configured for either series or parallel resonance.

[Evan K7FOS @k7fos]

I recently started learning to make active audio filters from opamps. This is the first one I've finished designing! It's a stereo low-pass filter (bass boost), with a 16kHz cutoff.

Sallen-key topology, dual-channel, 3x cascaded.

#maker #pcbdesign #audiogear

[Evan K7FOS @k7fos]

@JLCPCB There is a bug on your "payMethod" page that is preventing me from being able to check-out. Is this a known issue?

[Evan K7FOS @k7fos]

I accidentally assigned 0804 resistors for a 0603 footprint, resulting in them looking like crooked teeth. Whoops! I wish the assemblers had rejected the design, but surprisingly it still works! Nonetheless, these PCBs have become the "test batch."

[Evan K7FOS @k7fos]

@jhsu Dude. I need to know more. This is really cool. What does it do so far?

[Evan K7FOS @k7fos]

Progress!

[Evan K7FOS @k7fos]

Two new PCB designs! Colpitts oscillator and a 40dB RF preamp. The overall plan is to eventually build a radio transceiver block-by-block.

[Evan K7FOS @k7fos]

@Cluster_M @JLCPCB Oof, I spent way too long regenerating my gerbers, assuming it was something wrong on my end. Glad to know I just need to wait while they get it fixed up.

[Evan K7FOS @k7fos]

Initial magloop antenna assembly is complete! After testing it I think it could use a good coat of paint.

I need to make a larger coupling loop for it, but this'll do for now.

[Evan K7FOS @k7fos]

My quarantine project is coming along nicely! This is the controller for a magnetic loop antenna. It has a vacuum-variable capacitor that's controlled by a Raspberry Pi and stepper motor! I'm hoping to do the final assembly this weekend. 😁

[Evan K7FOS @k7fos]

Got the LCD library U8G2 to work with my design! Unfortunately, it isn't connected to the correct SPI pins, so I had to use the software implementation. This is making the screen refresh dreadfully slow... Oh well, one step at a time.

[Evan K7FOS @k7fos]

New project! It will be a battery-disconnect module that will auto-disconnect after a specified interval based on either a battery voltage-drop (as what happens when the engine shuts off) or errant power consumption, etc. Now to write the firmware...