Schematic review for Votage and current AC&DC monitor PCB - Page 1
Forum section: electronics / projects

author: huy
author_rank: Newbie
timestamp: December 06, 2024, 06:36:06 pm
content: Hi everyone,This is my first time designing a PCB. My PCB's function is to read the voltage and current of DC and AC voltage, control some relays, and read some input.So can you review it and give me some advice.Please ignore pin A0,A1 of INA219.Thank you.Sorry my English is not good

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 06, 2024, 08:48:37 pm
content: The opamps must be biased mid-supply

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 07, 2024, 04:55:58 pm
content: Correction;I see that you’re employing the LM358. The input’s common mode range is, Vcc-1.5 v. Same with the output’s Voh. These values are from memory, check the data sheet yourself.With a 5 volt supply this means you only have a signal range that will max out at 3.5 volt.If you do require the full 5 volts range, then you must use a rail to rail opamp.And I know, they do cost more than a LM358.

author: huy
author_rank: Newbie
timestamp: December 08, 2024, 05:04:51 am
content: Thank you for the feedback!You are correct that the LM358 has a common mode input range of Vcc-1.5V and an output range limited to approximately Vcc−1.5, which means the maximum output voltage would be around 3.5V with a 5V supply. However, in my case, I am interfacing the LM358's output with the ADC of a Raspberry Pi Pico, which only accepts a maximum input voltage of 3.3V. Therefore, the 3.5V maximum output of the LM358 is not an issue, as my circuit is designed to ensure the output does not exceed 3.3V for the ADC input.Thanks again for your input!When I connect A1 pin INA219 with SDA or SLC do I need a resistor?

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 08, 2024, 02:49:19 pm
content: Edit;With respect to the address lines, read carefully the device data sheet.Some devices allow open circuit pins as a third address. Otherwise they must be tied high or low, directly or through a resistor.2nd Edit. Since your range will be roughly between 0 and 3.5 volts, bias the opamps at 1.75 v.

author: jwet
author_rank: Frequent Contributor
timestamp: December 08, 2024, 11:47:17 pm
content: The opto inputs should take load resistor high to 5v and take the output from the collector.A dozen INA219's will make TI stock happy. If its a one off, its doesn't matter but measuring current in the analog domain and then inputting to your micro's ADC's would be a lot cheaper even if you had to add a nice external ADC. These parts are also quite slow- may not matter. You might consider filtering these input after then sense resistors, motors make a lot of junk on the rail.Those places where you have a divider on positive op-amp inputs for a pseudo ground, these nodes should be bypassed with a .1u to ground. Also, with 5v, you running out of headroom. Probable want to look at another amp or use larger supplies.You show a lot of 100pF bypass caps (INA V+), this should be 100nAre you sure the V/2 dividers are correct for left 358 amps- (eg r43 and r46)- I don't know what this is doing?It looks like you're using a PICO. I don't think the PICO is 5v compatible part- its a 3.3v part though it does have an onboard linear. Double check, I could be wrong. You have a level shifter for I2C and UART but the op amp inputs etc will exceed 3.3, etc.Be careful with layout of buck converter- LM2598. Copy eval circuit layout if available. This is somewhat advanced layout stuff.Good luck with your design- we all were beginners once. Have fun.

author: Benta
author_rank: Super Contributor
timestamp: December 09, 2024, 12:14:12 am
content: I took one look and ran away.I'm not going to go searching for labels between little boxes.Draw a proper schematic using wires/buses and remove the little boxes, then I might help.

author: jwet
author_rank: Frequent Contributor
timestamp: December 09, 2024, 01:11:34 am
content: just bored tonight I guess

author: huy
author_rank: Newbie
timestamp: December 10, 2024, 04:05:08 am
content: I recently bought two modules: the ZMPT101B and the INA219. Both are working well. I copied the schematics from these modules for my circuit, but I’m not sure if the schematics are correct.

author: huy
author_rank: Newbie
timestamp: December 10, 2024, 04:07:28 am
content: I've seen many schematics online that are similar to mine. Can you provide an example of a well-designed schematic?

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 10, 2024, 07:31:15 pm
content: Did you purchase them on Aliexpress?I searched for them and couldn’t find the device that you are showing.

author: SteveThackery
author_rank: Super Contributor
timestamp: December 10, 2024, 08:47:17 pm
content: Quote from: Benta on December 09, 2024, 12:14:12 amSeconded! "Connection by label" is lazy, and it leads to schematics which areverydifficult to follow. Searching for an occurrence of a particular label is exceedingly tedious, and what's worse is that there could be two or more occurrences (or there might not be), so you have to be hyper-vigilant in your search.Label-based schematics are OK for describing the circuit to KiCAD, but they aren't easily human readable.

author: Benta
author_rank: Super Contributor
timestamp: December 10, 2024, 10:40:58 pm
content: Quote from: huy on December 10, 2024, 04:07:28 amUnfortunately that's true. I don't know which clueless amateur with a website started this trend, but it's an abomination. And newcomers propagate the trend.

author: SteveThackery
author_rank: Super Contributor
timestamp: December 11, 2024, 11:20:42 am
content: Quote from: huy on December 10, 2024, 04:07:28 amIn the first one labels are used for the power and ground lines, but not much else. I'm not sure why the 24VCC line is highlighted, but you wouldn't normally do that. Note how you can follow all the signal paths easily, without having to search for labels.The second one looks horrendously complicated, but in fact is easier to follow than if extensive use of labels had been made. The signal flow can be followed directly, rather than having to search all over the diagram for labels.This is an important point: to you, that schematic probably looks scarily complex. But don't let that put you off. The question is, can you actually follow it? Can you trace the signal paths between the components? Can you see where the signal path splits to feed two components? Obviously in order to fully understand how it functions you need to look up the data sheets for the ICs, but that's true of a label-based schematic as well.In the third one, it uses labels, but (apparently) only for off-board connections. To the left of the diagram you will see how buses have been used to simplify the diagram without making it significantly more difficult to follow.I'm sure my examples will attract critical comments, but I just wanted to illustrate how even complex circuits can be drawn without widespread use of labels. In reality your circuits will be simpler than these to begin with. Here is a nice simple one.Back in the day it was common to draw the ground as a horizontal line along the bottom of the diagram (thus Vcc across the top, ground along the bottom, conventional current flow downwards from top to bottom). Nowadays it seems more common to replace the ground line with ground symbols. I think that's OK, and it allows for signal lines to travel underneath the other components, as you can see to the right in that final diagram.