can someone please check over my cricut design before i send the pcb to fabricat - Page 1
Forum section: electronics / projects

author: adenbob
author_rank: Contributor
timestamp: October 28, 2020, 05:53:03 pm
content: can someone look over my circuit diagram and pcb v2.2 as i had already sent v2.1 to get produced and released i didn't have a clock circuit for the chip. can someone look it over and make sure i'm not making any other glaringly obvious mistakes please.link to project:https://easyeda.com/adenandreana/eth-relay-v3

author: Renate
author_rank: Super Contributor
timestamp: October 28, 2020, 08:15:55 pm
content: Well, it doesn't affect your layout any, but...R3 should be higher than 100 ohms, maybe 470 or higher depending how much you want to scorch your eyeballs.R1 should be lower than 10 k if you are going to connect something external, maybe 2.2 k.You might throw a 0.1 µF to ground on that line too.Speaking of which you could use some of those on the Vcc too.You're not using this to connect/disconnect a CAT 5 cable, are you?

author: Yansi
author_rank: Super Contributor
timestamp: October 28, 2020, 08:20:47 pm
content: Wheres the flyback diode for the relays?Whats the purpose of this whole contraption?

author: adenbob
author_rank: Contributor
timestamp: October 28, 2020, 10:43:06 pm
content: please explain the capacitor on gnd and vcc do you mean that a cap will go across vcc and gndi will be using it to switch on and off an Ethernet connection it will switch the connection on at power up then once the enable switch is pressed it will disconnect it and wait indefinitely until it loses power.the reason i am using relays is because i have them lying around otherwise i wold be using a more practical solution

author: adenbob
author_rank: Contributor
timestamp: October 28, 2020, 10:43:45 pm
content: i do have a flyback diode on the pcb v2.2 it is near the mosfet on both the schematic and the pcb.

author: phil from seattle
author_rank: Super Contributor
timestamp: October 28, 2020, 11:01:35 pm
content: A suggestion, use DPDT relays, you can cut the number of coils in half.What is the current draw of those relays? Assuming they are 5V, I'd guess in the 50-100 mA range. So times 8 you are looking at 400 to 800 mA. What's plugged into your usb connector? Can it handle that kind of instantaneous draw? I wouldn't be surprised if the atmegashits the bedresets.

author: nuclearcat
author_rank: Unknown
timestamp: October 29, 2020, 12:05:47 am
content: Everybody forgot important wordEthernet?IMO, you can't route Ethernet like this. It is high frequency stuff.Most likely you can't route them over generic relays as well.

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: October 29, 2020, 12:16:36 am
content: From what I see you are trying to switch all the relays on at the same time, correct?The coil resistance of a 5V relay is fairly low. Not a problem for the FET, but maybe too much for the USB if that's where you are getting the power from.Are you missing some other wiring because you are trying to simplify or prove the circuit?Why do you need a 328 @ 16MHz to just do the push button switching?A simple Flip Flop with a Schmitt Trigger for the push button will save you a lot of power.

author: MarkF
author_rank: Super Contributor
timestamp: October 29, 2020, 12:32:33 am
content: You do realize that the RJ-45 ethernet connectors ONLY use two-pairs?You only need to break 4 wires.

author: nuclearcat
author_rank: Unknown
timestamp: October 29, 2020, 12:36:48 am
content: Quote from: MarkF on October 29, 2020, 12:32:33 amThats if you speak about 10/100Mbps. And even on 100, it is still diffpairs and preferable to respect that IMO (not sure how they tolerate such layout as on this PCB, i have little experience on that)And if it is 1Gbps it is more complex.

author: Renate
author_rank: Super Contributor
timestamp: October 29, 2020, 12:37:31 am
content: Quote from: adenbob on October 28, 2020, 10:43:06 pmYes, near the ATMega 328P.Quote from: nuclearcat on October 29, 2020, 12:05:47 amI didn't.This might take 2 pair or 4 pair dependent on which variant/speed Ethernet it is.Quote from: MarkF on October 29, 2020, 12:32:33 amWell 1000BASE-T uses 4 pair.Although you probably can't do switching easily on 1Gb/s signals using relays.I think I might try wiring it up as a "kill" rather than a pass.Have it throw a cap across a pair.

author: MarkF
author_rank: Super Contributor
timestamp: October 29, 2020, 01:05:50 am
content: I don't know if you could even get Gigabit Ethernet data through those relays...I would at least try to keep the twisted pair traces together across the PCB.

author: adenbob
author_rank: Contributor
timestamp: October 29, 2020, 01:29:31 am
content: to everyone concerned abt current i'm just using usb as a connector if i have to i can solder directly to the board i will be using a 1 amp wall wart to paower itand to those concerned about the connection speed i don't really care how fast it actually is as long as i can get 10mbps and i had made a vashon 1 an it gives me 100mbps speeds thru relays Ethernet is surprisingly robust even with shtty conetionsyes they are all operating togetherwhat cap value wold you recommend for the vcc to gnd

author: Renate
author_rank: Super Contributor
timestamp: October 29, 2020, 01:34:06 am
content: I've got a better idea.Use an inexpensive ethernet hub/switch.This is a random cheap one (uses 230 VAC):https://www.amazon.com/Ethernet-Splitter-Optimization-Unmanaged-TL-SG105/dp/B00A128S24Then you just need to switch power to it.Edit: Or even simpler if you can locate the reset circuit internally then you only need a logic signal instead of a P MOSFET.Or even the enable on the DC converter.You might even find space inside the case to put your little circuit (and you wouldn't need a USB supply).You might look at simpler AVR8 chips like ATTiny85 if you just want on/off buttons.

author: adenbob
author_rank: Contributor
timestamp: October 29, 2020, 01:46:42 am
content: i'm just using a atmega328p-pu because i have a few extras with the arduino bootloader already

author: nuclearcat
author_rank: Unknown
timestamp: October 29, 2020, 02:30:25 am
content: One more important thing. How you are going to program your atmega? I dont see ICSP connector.

author: adenbob
author_rank: Contributor
timestamp: October 29, 2020, 02:45:32 am
content: im going to program it in a zif programing shield for the ardunio uno then put it in a socket in the board

author: uski
author_rank: Frequent Contributor
timestamp: October 29, 2020, 05:03:45 am
content: Quote from: adenbob on October 29, 2020, 02:45:32 amI would recommend that you add ICSP headers. It is going to make your life so much easier.Also, for D2 I recommend you use a 1N4007 (stronger diode). I have seen product failures due to 1N4148 failing after a few months when used with a relay like this. And 8 relays at the same time, packs quite a punch for this poor little diode.What is the use case for this system ? I understand you want to plug/unplug an Ethernet cable, but maybe there is a better solution.For instance you could purchase an Ethernet switch and control its switch circuit over I2C. I've seen multiple unmanaged ethernet switches which actually had a manageable chipset inside, with the I2C port unconnected (or connected to an EEPROM for static settings). It would give you a 4-way Ethernet relay, much cleaner, much more versatile, with no signal degradation whatsoever.PS: I would also add a 100nF capacitor to ground from #RESET of the MCU, which will create an RC circuit that will ensure the MCU is reset when power is applied.Also, what is the trigger condition to control the relay ? Is it like a timer ?You can also probably drop the pullup resistors for the switches and use the integrated pullups in the microcontroller.

author: uski
author_rank: Frequent Contributor
timestamp: October 29, 2020, 05:06:58 am
content: Quote from: adenbob on October 29, 2020, 01:46:42 amWell if you care about the Arduino bootloader, add a USB to TTL header on your PCB so that you can program your board directly from the Arduino IDE !You can add just the header and use an external USB to TTL FTDI (or equivalent) cable. Or the full USB circuitry on your board (more complex - up to you).Don't forget to wire the reset pin. Then GND, RX and TX and it should be enough I think.Otherwise the Arduino bootloader is useless. Just put a 6 pin ISP header and use a cheap USB programmer (example)

author: Renate
author_rank: Super Contributor
timestamp: October 29, 2020, 11:51:11 am
content: Quote from: uski on October 29, 2020, 05:03:45 amInternal pullups are on the order of 70 k.I don't even like to have that high impedance on a push button in a grounded metal case.I like my switches to have a milliampere or two through them.Since this project has a remote switch on a jack I sure wouldn't want a 70 k impedance line flapping in the breeze.

author: adenbob
author_rank: Contributor
timestamp: October 29, 2020, 04:45:46 pm
content: the trigger condition is energise on power up then wait for user input in the form of pressing the enable button then wait an infinite time

author: adenbob
author_rank: Contributor
timestamp: October 29, 2020, 05:04:01 pm
content: Quote from: uski on October 29, 2020, 05:03:45 amim not to concerned abut d2 as this curcut should only be switching on/off at most once a month, if i have to i can throw a extra chunky rectifier diode

author: Renate
author_rank: Super Contributor
timestamp: October 29, 2020, 08:41:04 pm
content: If you're really going to persist in making this with relays...Determine if you need 2 pair (4 wires) or 4 pair (8 wires).UseDPDTDPST relays and keep them each on a single pair.Maybe even try this (at least the relay and connectors) on a perfboard to see if it's even going to work?How about a mechanical arm that mates and un-mates a RJ45 into a socket?

author: uski
author_rank: Frequent Contributor
timestamp: October 30, 2020, 05:49:56 am
content: Quote from: adenbob on October 29, 2020, 04:45:46 pmIt seems to me you can add a single relay and perform the same task. No need for a microcontroller for thisJust a switch and a dual pole relay

author: S. Petrukhin
author_rank: Super Contributor
timestamp: November 02, 2020, 01:58:53 am
content: Quote from: adenbob on October 29, 2020, 04:45:46 pmEthernet 10/100 works on 2 pairs, no need for 8 relays.It operates at a carrier frequency of 32MHz - it is not nice to switch it with a conventional relay. It may work, but it's not reliable.