why the output of max232 is like this? - Page 1
Forum section: electronics / projects

author: navidrct
author_rank: Regular Contributor
timestamp: August 27, 2015, 09:24:47 am
content: hii fed 40Khz to max232 and it give me nothing but DCu can see the circuit and input and output in attachment

author: DJohn
author_rank: Regular Contributor
timestamp: August 27, 2015, 09:36:56 am
content: It's a bit hard to read the scope, but it looks like the input is under 1.5V. VIH is 2V, so it's seeing your square wave as a constant 0. The driver is inverting, so the output will be the constant high voltage you're seeing.

author: krish2487
author_rank: Frequent Contributor
timestamp: August 27, 2015, 09:39:45 am
content: Ummm, because you are not trying to use it properly.Refer to the typical application circuit, and the components, values used, read the fine print and then breadboard it.The data sheet is, generally speaking, an invaluable tool to start reading first.

author: krish2487
author_rank: Frequent Contributor
timestamp: August 27, 2015, 09:41:28 am
content: What he is seeing on the scope is a improperly working charge pump. Improper capacitor values. The datasheet recommends 1uF cap for the charge pump. He is using 150nF.Quote from: DJohn onTodayat 07:36:56 PM

author: navidrct
author_rank: Regular Contributor
timestamp: August 27, 2015, 09:42:48 am
content: thanks a lot.I use my MAT of LPC1768 to generate 40 KHz .i should try PWM . maybe that reach the max232 limit .

author: navidrct
author_rank: Regular Contributor
timestamp: August 27, 2015, 09:46:26 am
content: plz see this .it works for him.

author: navidrct
author_rank: Regular Contributor
timestamp: August 27, 2015, 09:49:44 am
content: see thishttp://uglyduck.ath.cx/ep/archive/2014/01/Making_a_better_HC_SR04_Echo_Locator.html

author: JoeO
author_rank: Frequent Contributor
timestamp: August 27, 2015, 10:04:38 am
content: Uglyduck is using a 232A. You are using a 232.

author: ConKbot
author_rank: Super Contributor
timestamp: August 27, 2015, 10:08:19 am
content: Stahhhhhp with the schematics with no wires and just net labels connecting things, it's bad practice and makes stuff hard to follow.

author: navidrct
author_rank: Regular Contributor
timestamp: August 27, 2015, 10:16:50 am
content: Quote from: JoeO on August 27, 2015, 10:04:38 ami don't know if there is big different between them . i will change the 150 nf to 1 uf . i hope it work

author: navidrct
author_rank: Regular Contributor
timestamp: August 27, 2015, 10:17:34 am
content: Quote from: ConKbot on August 27, 2015, 10:08:19 amsorryit make life so much easier

author: navidrct
author_rank: Regular Contributor
timestamp: August 27, 2015, 10:34:21 am
content: Quote from: krish2487 on August 27, 2015, 09:41:28 ami change it to 1uf but no change in output

author: mikerj
author_rank: Super Contributor
timestamp: August 27, 2015, 04:09:46 pm
content: Quote from: navidrct on August 27, 2015, 10:34:21 amDid you increase the input voltage swing to ensure it exceeds the 2v threshold?

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: August 28, 2015, 12:13:42 pm
content: I would say it has to do with the output impedance of the transducer that you are trying to use. What is it? Then look at what the other circuit is using. It looks like a piezo at the rated frequency. I hope you are not using a low resistance speaker of any kind. And the 232A is a different animal, look at the datasheet.

author: krish2487
author_rank: Frequent Contributor
timestamp: August 29, 2015, 04:16:45 am
content: It could be anything, not enough information to help us help him.It could be as simple as the same PWM signal on both the lines to not enough threshold voltage to meet the Vlow Threshold to improper charge pump caps to Max 232 /232AIt literally could be anything.