I am designing a PCB which uses a  DPDT relay. I actually only need one of the relay contacts, but this relay was cheaper than any equivalent SPST relay I could find. Is there any advantage to connecting the second relay contact either in parallel (as shown in the picture) or in series? Or would it be better to just use one contact and leave the second unconnected?    I already know that connecting in parallel will not allow me to double the amount of current the relay can handle, since the two contacts might not switch at the exact same moment. One advantage to connecting in parallel I could think of is that if one of the contacts eventually became stuck open, the circuit would still work as long as the other contact still worked. However, if the contacts were more likely to become stuck closed rather than open, it would actually be better to connect them in series instead. Is one of these modes of failure more common in this type of relay, or is there any other advantage to either connecting the second contact in parallel, series, or not at all?  Edit: This relay is used as an auxiliary dry contact output. The user can connect the relay contacts to another device in order to trigger it to do something. The relay will be triggered by some sort of event, turn on for a configurable amount of time (usually no more than a few seconds), then turn off again.
122648
I'd like to control a 20 amp, 240 volt AC resistive load with a heavy duty contactor.  The contactor I have is a Siemens 3TX7130-0DB03 rated for 30 amps, and DPDT.  I was originally going to switch both lines on this relay.  But I got to thinking...  Would it be easier on the contactor to use both poles in parallel to switch the same line, and leave the other line always powered? What theory or research would support that conclusion?  In short...       &ndash; Schematic created using   Which of the above relays will last longer, why, and what other pros and cons are there?
19314
This is probably a very basic question but I have the following circuit, I am not sure what is in series and what is in parallel or if they are all in parallel, initially I thought R2 and R3 were in series and then used the sum of their resistances with R1 to calculate the equivalent resistance, that seems to be  off based on some circuit simulation software I am using so I would appreciate if somebody could explain how to calculate the Rt and the logic behind it.  Thanks.          &ndash; Schematic created using
92156
I've seen tutorials aimed at beginners suggest the way to drive an LED from something without enough current drive is this:   (option A)  but why not this:   (option B)  Option B seems to have some advantages over option A:   fewer components the transistor does not saturate, leading to a faster turn-off the base current is put to good use in the LED, instead of making the base resistor warm   and the advantages of option A seem to be few:   brings the load closer to the supply rail   but when Vcc is significantly greater than the forward voltage of the LED, this hardly matters. So, given these advantages, why would option A be preferred? Something I'm overlooking?
21560
In most electrical circuits with a relay, a diode is connected in parallel to the coil of the relay. Why? Is it always a good practice?
47105
I've read up a little bit on bonding nics with ifenslave; what I'm having trouble understanding is whether there is special configuration needed in order to split the bonds across two switches. For example, if I have several servers that all have two nics each, and two separate switches, do I just configure the bonds and plug 1 nic from each into switch #1 and the other from each into switch #2? or is there more to it than that?  If the bonds are active-backup, will a nic failure on single machine mean that server may become disconnected since the rest of the machines are using the primary nic and it's using the secondary? Or do you link the switches with one cable as well?
107456
Two or more capacitors are said to be connected in parallel if each one of them is connected across the same two points. In a parallel combination of capacitors potential difference across each capacitor is same but each capacitor will store different charge. Why is this true? Why is the potential difference across each capacitor in parallel the same and why will each capacitor store different charge?  Also, in series, why are Potential difference across each capacitor different, while charge is the same?
17803
In the circuit the relay is controlled from a manual switch on a 12v bus. I can't understand why you would want to add the extra components of the transistor and diodes to the circuit? ie why are D4, R1, T1, D1 needed? Thinking about cost and component count here.
50065
On our circuit breaker, we have several circuits that are linked together by a metal handle. For instance, there are several cases of three 20A circuits all linked together, meaning you can only flip all three at once. Does that mean those three 20A circuits equal 60A? If not, what is the purpose of having multiple circuits linked together?
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Generally relay triggers when current passes through its coil. When current stops flowing, moving terminal of relay is pulled back into the default situation. I need relay, once triggered, to remain in that situation only regardless of the current. In short, I want the relay without spring. I am pretty sure that this kind of relay doesn't exist, but there must be a component which satisfies this requirements. I mostly work on Digital and FPGA side, so I don't have enough knowledge about Analog.If anyone can suggest me a component which fits here, it will be very helpful for me
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I've been taking apart a recent, standard touch tone phone with the aim for automated dialing via a separate MCU with transistors activating the contacts (Smirk. An assistive technologies project designed for my grandmother, not 'robo-calling').  Removing the solder mask it is quite clear how to accomplish this in this case--   However, I had another question: Namely, does anyone know what process/method is being used here to trigger the switches ?  Rather than any physical device, the button contacts seem to be overlaid on the board themselves with a type of 'black substrate'. No visible connections are already apparent between the buttons.  At first I thought perhaps captive touch, but then they are activated by basically a rubber pad on the matching side, plus a plastic 'number button' on top.  My second thought here was that somehow the button press might be creating 'arcing'-- but could the voltage really be so high in this case?  I wondered if anyone had any thoughts as to what is going on, or what process is being used?
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Long time reader, first time poster. Working on updates for our new house and I bought a few lutron caseta switches the other day to wire up in our front entryway. I went with the PD-6ans which requires a neutral wire. I pulled the plate off and looked around and saw a neutral bunch so I thought I was good to go.   Well, like any project I get myself into, things didn't go as planned. The two switches on the left come from one circuit with the neutral bundle, the switch on the right is on a different circuit and there's no neutral.  Can I use the neutral bundle from the other circuit in the box or is that a big no-no? If not, is there any other way to get around it?  I'm thinking I may just need to buy a different switch that doesn't require a neutral (Lutron Caseta PD-5WS).  Here are a few pictures of the three gang box. It's a three way switch on the far right and left, single pole in the middle. For what it's worth, at the other location (in the garage) for the three way on the right there does appear to be a neutral bundle.   Also, there's a ground wire that doesn't go anywhere from that far right switch. Should I pigtail it into the ground wire bundle in the box that is in the other circuit?   Thanks for any help you can provide!
100162
I just bought a 5 volt dual relay module for my arduino.  But now that I have it I was wondering if there is any way that I could control it directly from USB.    The pinout of the module is GND  ONE  TWO  VOC This would make it really easy to just connect a USB cable to it. Assuming I did that is there any way to send 5 volt through the USB Data+ and Data-?  Thank you
86877
I am working on an MSP430 project that requires me to route the output of one peripheral into the input of another peripheral. Thus, I have two MCU pins connected directly to each other. This looks suspicious to me since there is the possibility of a programming error causing both to be (possibly conflicting) outputs. Also, there is the issue of startup and programming states.  In the worst case, if one pin is driving HI, the other is driving LO, the GPIO pins generally have way more sink capability than source capability... so it'll be somewhat like taking a HI output and shorting it to near-ground. Which is bad... but how bad is it? Is it likely to cause damage to the MCU?  I often see examples on the web of people using Arduinos to light an LED between two pins without a resistor, and I haven't heard of any stories of anyone frying anything but the LED. Clearly you wouldn't want to do this in a product, but do manufacturers generally try to protect the MCU from GPIO pins being overloaded anyway?  Thinking about it in retrospect, putting a current-limiting resistor between the two pins would have prevented any worries, but even a minor hardware change is a very difficult thing to do at this point.  For future reference and the benefit of posterity, does anyone have any other ideas about the proper way of minimizing the risks of connecting two MCU pins together, and more generally, minimizing the risks that come from the possibility of overloading a GPIO pin?
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Is there a reason, beyond historical reasons, that three phases has become the dominant number of phases?  I am aware of the advantages against one phase and two phase, namely the reduced amount of conductor needed, and that motors can provide torque when stalled (and less pulsation).  Is this solely due to diminishing returns, with only a small increase in smoothness of torque application, at the cost of increased complexity (increased number of wires (albeit of smaller CSA)).  To be clear, the phases are all evenly distributed, that is, five phases separated by 72 degrees.
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This is subjective per say. But I am looking for other peoples experience.  If I am going to screw eight wires into daughter relay board's terminal block, is there a benefit or advantage to tinning the copper end before?  The environment that the units are to be installed is not near the coast and is not normally damp/wet. Rather dry and hot.
64789
So I'm wondering if anyone has any information about the Dell power supplies which have 3 contacts on the barrel.    I know the 3 are power, ground, and some sort of communication link. Does anyone know what the communication line is for and/or what kind of protocol it uses?  Thanks  EDIT The reason I ask is I'm considering trying to build my own semi-advanced charger (not for a laptop but something else... it's a long story) and while I'm sure I could figure out a charging circuit given the internet as a resource, I was wondering what they use the communication line for and if it's necessary for my purposes. It seems the answer is no since I will be the only one using my device and thus don't need to worry about people plugging in not kosher chargers...
91626
I use a 7805 for a project where the circuit needs a higher current (~2.8&nbsp;A) at 5&nbsp;V. So I assume that if I use both ICs in parallel I can increase the maximum current capacity. Would it work?