Question about "Bat detector" / frequency shifter - Page 1
Forum section: electronics / beginners

author: Vtile
author_rank: Super Contributor
timestamp: December 23, 2021, 12:13:07 pm
content: Hi.I must ask before re-inventing the wheel. Is there a working frequency shifter circuit for ultrasound spectrum types around (as public domain / de facto standard etc.)(like something based on simple discrete ICs, not uCU). I don't know where and what to search for.Google will give 'zillion' circuits for bat detector, but I rather not to try to lit a led, but would be more interested actual frequency shifting I'm in impression that there is some clever circuits for it hoovering around in analog domain or analog+digital hybrids. Which I could then adapt to my hobby project (with different degrees of success).I'm not knowledgeable enough on subject to ask if there is different types, working principles or "quality levels of sound conversion" on these.OPAs and discreet parts preferred, uCU if analog part count is measured in kilograms.edit. OK. It seems there is a few "basic designs" hovering around, with somewhat decent sound conversion (realistic or not). One is published in elector in nov 2011 and for that there is many $20 kits around, then there is some other similar designs with actual sound samples. Most seems to be based on digital counter and have 2 to 3 ICs.

author: radiolistener
author_rank: Super Contributor
timestamp: December 23, 2021, 12:57:51 pm
content: You can use some mixer circuit which allows to works from DC frequency. For exampel -AD831.Here is Chinese DIY module with AD831 on aliexpress:https://www.aliexpress.com/item/32798750251.htmlI have this module and just tested it with signal generator and headphones - it works. I can hear sweep from 30500 Hz to 35000 Hz.Here is some technical details:Power supply: 9.00 VRF input: ultrasonic sound 20-40 kHz, amplitude 0.05 VLO input: 30 kHz sine with amplitude 0.1 VIF out: connected to stereo headphonesWhen RF input amplitude is more than 0.05 V, the output is distorted. It still works up to 0.5 V, but you can definitely hear clipping artifacts. So, I recommend to put signal with amplitude below 0.05 V. I connected output directly to 8 Ω stereo headphones and can hear signal. Not loud, but enough to hear it. For a weak signals you can add amplifier on the IF out.In this case I shift down frequencies from 30 kHz (LO input) to zero frequency. So I can hear 30-40 kHz as 0..10 kHz and 20-30 kHz as 10..0 kHz.

author: Vtile
author_rank: Super Contributor
timestamp: December 23, 2021, 01:00:24 pm
content: Quote from: radiolistener on December 23, 2021, 12:57:51 pmOh, I will need to look on that also ! Thanks.

author: radiolistener
author_rank: Super Contributor
timestamp: December 23, 2021, 01:10:33 pm
content: With this AD831 Chinese module you can experiment with frequency shifting from DC to 500 MHzAll what you need is LO generator which frequency will define frequency shift.Be careful with power supply, don't exceed 9V.And be careful with RFin and LOin inputs, the max allowed amplitude is just 1 V. Don't exceed it. In order to protect these inputs, you can put two antiparallel diodes, to limit amplitude. For such purpose use diodes which opens at 0.6...0.8 V.PS: In order to cover full bat bandwidth (20-150 kHz) you can use square wave on LO. Square wave consists of harmonics and each harmonics will be used to shift frequency down to zero. So, several bands will be mapped into audible 0..20 kHz simultaneously

author: nali
author_rank: Frequent Contributor
timestamp: December 23, 2021, 01:20:30 pm
content: Here's a bit of material to keep you amused...https://github.com/DD4WH/Teensy-Bat-Detectorhttps://www.teensybat.com/I've been looking at doing the same for a while but I'e already got too many projects on my to-to list

author: Zero999
author_rank: Super Contributor
timestamp: December 23, 2021, 07:08:49 pm
content: https://www.eevblog.com/forum/projects/want-to-hear-the-bat-flying-in-my-front-yard/