---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 03/20/24: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:37 AM - LM386 Output Capacitor (user9253) 2. 08:27 AM - Re: LM386 Output Capacitor (Charlie England) 3. 08:58 AM - Re: LM386 Output Capacitor (user9253) 4. 04:40 PM - Re: LM386 Output Capacitor (user9253) ________________________________ Message 1 _____________________________________ Time: 06:37:54 AM PST US Subject: AeroElectric-List: LM386 Output Capacitor From: "user9253" Radio Shack's Engineer's Notebook by Forrest Mims is my favorite book. One page is devoted to the LM386. I made the "Audible Alarm". I question the value of the 22 microfarad output capacitor because all of the other LM386 circuits on that page use 220F output capacitors. Could that be a typo in the book and the value should be 220F? I used three 10F capacitors in parallel and the alarm works. Would it work better with a 220F capacitor? I increased the value of C1 to 1F to get a lower pitched tone. Are there any other suggestion for getting a lower pitched tone? I have trouble hearing high frequency tones in my old age. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=513398#513398 Attachments: http://forums.matronics.com//files/audible_alarm_841.png ________________________________ Message 2 _____________________________________ Time: 08:27:18 AM PST US From: Charlie England Subject: Re: AeroElectric-List: LM386 Output Capacitor On Wed, Mar 20, 2024 at 8:40=AFAM user9253 wrote: > > Radio Shack's Engineer's Notebook by Forrest Mims is my favorite book. > One page is devoted to the LM386. I made the "Audible Alarm". > I question the value of the 22 microfarad output capacitor because > all of the other LM386 circuits on that page use 220=C2=B5F output capaci tors. > Could that be a typo in the book and the value should be 220=C2=B5F? > I used three 10=C2=B5F capacitors in parallel and the alarm works. > Would it work better with a 220=C2=B5F capacitor? > I increased the value of C1 to 1=C2=B5F to get a lower pitched tone. > Are there any other suggestion for getting a lower pitched tone? > I have trouble hearing high frequency tones in my old age. > > -------- > Joe Gores It's been a really long time since I played with R-C filter formulas, but I'd bet that they went with 22 instead of 220 because they didn't need low frequency audio performance from the circuit. IIRC, the out capacitor sets the low frequency cutoff for the output. It's a 'point design' for a single, high frequency tone. IIRC, the LM386 is basically a high current opamp. I'd suggest downloading a copy of either the TI or National analog IC 'cookbook' to see circuits. Here's a 1kHz square wave oscillator from the TI LM386 datasheet : [image: image.png] The square wave will give a 'nastier' more irritating tone, which is what you'd want for an alarm. Virus-free.www.avast.com <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> ________________________________ Message 3 _____________________________________ Time: 08:58:36 AM PST US Subject: AeroElectric-List: Re: LM386 Output Capacitor From: "user9253" Thanks for that circuit Charlie. I will give it a try. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=513400#513400 ________________________________ Message 4 _____________________________________ Time: 04:40:29 PM PST US Subject: AeroElectric-List: Re: LM386 Output Capacitor From: "user9253" I made the Texas Instruments square wave oscillator, substituting a speaker for the load resister. It works but with a high pitched tone. So then I went back to Forrest Mims' alarm circuit and put a 10F capacitor in parallel with C1. Now I am satisfied with the deeper tone. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=513401#513401 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.