This project is based on the Explorer E202, with permission.

Renato Romero put plans online for a Very Low Frequency (VLF) receiver capable between “a few Hz to beyond 10 kHz [which] makes it suitable to to receive radio signals of natural origin; signals not generated by human activity but by physical phenomena such as lightning and solar storms. Received signals are heard directly in your headset. The receiver amplifies the electric component of an electromagnetic signal.”

His plans are described here. The Explorer E202 is no longer available for sale.

He gave me permission to work from his schematic to design a new layout and make my own units. I am releasing all of my documents and process under the CERN Open Hardware License v1.2.

Here’s the original E202 full-size schematic.

Assembled v1.1 Receiver with Case

A fully assembled v1.1 in a box looked like this:

Assembled v1.4 Receiver Board

The final board for v1.4, which is the release version, looks like this:

Cost

Total cost of parts is about $25 if you order minimums. It’s about $100 if you go to the next price break for most at qty=10, which is what I did since I’m prototyping, and what I recommend if you want to build two or more units.

OSH Park: $35.35 for a set of three bare boards [Shared Project #NvQSoarW]

Digikey cart: $24.40 for parts for one board [Shared Cart #32fqdm]

You can get the documentation PDF, an uploadable Digikey .csv file, and the board manufacturing files in this zip file.

Bill of Materials

Ref Qty Description Digikey PN
BNC1 BNC2 BNC3 3 CONN BNC JACK R/A 50 OHM PCB A97555-ND
C1 1 CAP CER 0.033UF 50V C0G RADIAL 445-8490-ND
C10 1 CAP CER 10000PF 50V C0G RADIAL 445-8384-ND
C15 C14 2 CAP CER 0.022UF 50V X7R RADIAL 399-14089-1-ND
C16 C7 2 CAP CER 4700PF 50V C0G RADIAL 445-8585-ND
C2 C11 2 CAP CER 0.1UF 50V C0G RADIAL 445-8532-ND
C3 1 CAP CER 8.2PF 50V NP0 RADIAL 399-8923-ND
C5 1 CAP CER 150PF 50V NP0 RADIAL BC1015CT-ND
C6 C12 C4 3 CAP CER 10UF 16V X5R RADIAL 445-8290-ND
C9 C13 2 CAP CER 100UF 6.3V X5R RADIAL 445-8441-ND
D1 D2 2 DIODE GEN PURP 50V 1A DO41 1N4001-TPMSCT-ND
D3 1 LED BLUE CLEAR 5MM ROUND T/H C503B-BCS-CV0Z0461-ND
J1 J4 2 CONN PWR JACK 2.5X5.5MM HIGH CUR PJ-202BH
J2 J5 2 CONN TERM SCREW GREEN 2.54MM 2POS TH ED10561-ND
J3 1 CONN JACK STEREO R/A 3PIN 3.5MM CP1-3523N-ND
L1 1 FIXED IND 3.3UH 575MA 300 MOHM 78F3R3J-RC-ND
LAMP1 1 LAMP NEON 6.2MM WIRE TERMINAL A9A-ND
Q1 Q2 2 TRANS NPN 45V 0.1A TO-92 BC547BTACT-ND
R10 1 POT 10K OHM 1/5W PLASTIC LINEAR 987-1301-ND
R11 1 RES 4.7K OHM 1/4W 5% CF MINI S4.7KQCT-ND
R12 1 RES 2.2K OHM 1/4W 5% CARBON FILM CF14JT2K20CT-ND
R13 1 RES 1K OHM 1/4W 5% CF MINI S1KQCT-ND
R4 1 RES 3.3K OHM 1/4W 5% CARBON FILM CF14JT3K30CT-ND
R5 R1 2 RES 10M OHM 1/4W 5% CARBON FILM CF14JT10M0CT-ND
R6 R2 R3 3 RES 100K OHM 1/4W 5% CARBON FILM CF14JT100KCT-ND
R7 1 RES 10 OHM 1/4W 5% CARBON FILM CF14JT10R0CT-ND
R8 1 RES 10K OHM 1/4W 5% CF MINI S10KQCT-ND
R9 R17 2 RES 33 OHM 1/4W 5% CARBON FILM CF14JT33R0CT-ND
U1 1 IC REG LDO 9V 1A MC7809 TO220AB MC7809CTGOS-ND
U2 1 IC VREF GND REF ADJ TO92 296-6549-5-ND
U3 1 IC AUDIO PWR AMP LOW VOLT 8-DIP NJM386D-ND
U4 1 IC OPAMP JFET 3MHZ DIP8 296-7203-5-ND

Gerber Preview

Assembly Diagram