Schematic design critique - Page 1
Forum section: electronics / projects

author: Skyland
author_rank: Contributor
timestamp: March 13, 2015, 11:30:32 pm
content: I designed a schematic for my project and I'd be thankful if you could give me any feedback on it.I'm specially looking for anything wrong or inefficient with my circuit.The purpose of this project is to read data from the accelerometer, perform signal processing and output an alarm sound if a certain behaviour is detected.

author: Niklas
author_rank: Frequent Contributor
timestamp: March 14, 2015, 01:10:18 am
content: One specific thing: Arrange and group the component's name and value. In Eagle you can use the smash function to make it possible to move the name and value strings independently of the component symbol.

author: Hideki
author_rank: Frequent Contributor
timestamp: March 14, 2015, 02:09:15 am
content: The datasheet says that SMT-0540-S-R is a 12 (+/- 2) ohm transducer. At 3.3V that's 275 mA, which is way too much to drive directly from the atmega outputs.

author: Skyland
author_rank: Contributor
timestamp: March 14, 2015, 02:18:48 am
content: what kind of transistors would you recommend to amplify the current?Would it be useful to add 2 10uF capacitors to the speaker?

author: Hideki
author_rank: Frequent Contributor
timestamp: March 14, 2015, 02:31:42 am
content: http://www.atmel.com/Images/AT88CK109STK3%20User%20Guide.pdfSee Figure 3 on page 27 for how Atmel is doing it.

author: Skyland
author_rank: Contributor
timestamp: March 14, 2015, 02:44:16 am
content: Quote from: Hideki on March 14, 2015, 02:31:42 amBrilliant thanks, how about the coupling capacitors?

author: Hideki
author_rank: Frequent Contributor
timestamp: March 14, 2015, 02:51:21 am
content: What for? Protection against DC in case the MCU gets stuck? Well, maybe, but then why not put it before the transistor? Why you want to use two of them I don't know.

author: matseng
author_rank: Frequent Contributor
timestamp: March 14, 2015, 03:38:46 am
content: Not a design comment, but rather on the schematics.The lack of a power-arrow on the 3.3v for the R3/R5 pullups and also the ADXL makes me confused when looking the schematics quickly. If something is connected to vcc use a power-arrow, and use a ground-bar for gnd/vss.

author: Skyland
author_rank: Contributor
timestamp: March 14, 2015, 12:07:49 pm
content: Quote from: Hideki on March 14, 2015, 02:51:21 amBecause I am driving both pins of the speaker, none is connected to GND.

author: free_electron
author_rank: Super Contributor
timestamp: March 14, 2015, 03:02:32 pm
content: Whats up with all the nenames that sit half a mile off the wires they belong to?Whats up with the slanted wires ?

author: Zero999
author_rank: Super Contributor
timestamp: March 14, 2015, 07:25:34 pm
content: Quote from: Skyland on March 14, 2015, 12:07:49 pmThen you need to drive it with an h-bridge.It's best to use emitter followers and AC couple them to the MCU inputs.

author: Skyland
author_rank: Contributor
timestamp: March 15, 2015, 03:47:03 pm
content: Quote from: Hero999 on March 14, 2015, 07:25:34 pmI have changed the buzzer circuitry by adding a transistor to drive the magnetic buzzer.

author: PeterFW
author_rank: Frequent Contributor
timestamp: March 15, 2015, 04:04:05 pm
content: Quote from: Skyland on March 15, 2015, 03:47:03 pmThere is no need to use a shottky diode, at this load you can use allmost every diode you got at hand. Use the next best 1N00-something diode you can get.You do not state the battery voltage, if it is low enough connect the speaker directly to the battery supply if possible.And you should, if possible, replace the diode in the battery power path to the voltage regulator with a FET if the diode is only used to prevent a reverse battery connection.