Tagged Questions

Allowing for the flow of power or information without shared electrical nodes

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0
votes
0answers
92 views

Isolating Probe from stray voltage

I have a PH Probe taking readings from an ungrounded container that has sources of electrical noise (AC Pumps, AC heaters, etc). I would like to protect the probe from that noise. If the ...
0
votes
0answers
513 views

RS232 Ground-Loop Isolation: “creative” solution?

I have a RS232 connection that seem to suffer from different ground potentials at the two ends of the connection: The receiver signals a "break condition" in Realterm. As I understand it this means ...
1
vote
1answer
115 views

Ground coupling a high voltage source with the A_GND and D_GND

I have a device that measures the current in the mains through a 0.01 Ohm 20W shunt resistor. The voltage across the shunt is amplified by a op amp and feed into a uC's ADC for farther calculations. ...
2
votes
1answer
204 views

How do I (optimally) connect Elk-924 (high sensitivity relay board ) to DSC PGM output (sinks to ground)

This sounds like a very specific question, but I think it boils to a generic one -- not at all specific to this equipment. But it will take a bit of backstory to get there. My background, btw, is ...
2
votes
0answers
103 views

Isolation between cells for battery charging & testing

I want to charge Lipo battery packs and possibly other chemistries too. Six cell packs for starters. But hope to handle more and less. Perhaps a lot more cells. For electric vehicles, skateboards, ...
4
votes
2answers
249 views

When is it appropriate to galvanically isolate components/subsytems?

As the question implies, how do you determine when it is appropriate to galvanically isolate parts of the same electrical system from one another? For example, I'm currently constructing a tube ...
2
votes
0answers
469 views

How to isolate low voltage control circuit from high voltage power circuit?

Can anyone give me a brief run-down of some methods I could use for this? I want to drive a MOSFET or BJT with a 12v 555 circuit or oscillator. The MOSFET will drive a high voltage circuit that ...
0
votes
1answer
1k views

Effect of an isolation transformer on leakage current

How do isolation transformers affect the leakage current through protective earth in a system? Scenario 1: Mains is directly connected to circuit. Metal enclosure has a protective earth connection ...
3
votes
3answers
345 views

Mains triac safety circuit design

I am investigating using a triac instead of a relay to control 250V 10A devices. However all the 600V 16A triacs come in TO-220 packages. According to AS/NZS 3100 and AS/NZS 60335.1 I need at least ...
2
votes
1answer
150 views

How can I isolate a power well to reduce noise

I am designing a digital board which will drive a very coarse (simple on-off) high[er] current speaker. I am worried that the switching of the speaker will cause noise in the power supply driving it. ...
3
votes
3answers
248 views

DC-DC isolation for my car stereo… Where do I start?

I recently noticed that my jeep's stereo whines with a frequency that seems proportional to the rpm of my engine (and alternator), and is louder when my headlights are on. If my stereo was powered ...
1
vote
2answers
149 views

Dirt cheap 3-12v DC/DC isolatior chip?

I'm creating a box that will have an external TTL trigger. I want to isolate my box's power/ground from that of the triggering device. Obviously, an optoisolator is the way to go (eg. PS2502). ...
1
vote
1answer
286 views

GPIO input connected to garage door button

I know there are other GPIO / Garage door related questions, but this is not a duplicate- I need to read the status of the garage door button, not a garage door sensor. I would like to connect the ...
3
votes
1answer
253 views

USB + Power: Isolate or not?

I am working on an adapter that will allow a device to be connected to both a PC and external power supply. I am wondering if I will need to isolate the 2 5V supplies with a DC/DC converter and some ...
2
votes
2answers
1k views

How can I do A/D conversion with isolation?

I have to sense a voltage range of 0-25V dc and send to the ATMEGA 32 microcontroller. I want to use a voltage divider for sensing the voltage. But the problem is isolation is required between the ...
5
votes
3answers
188 views

Digital Isolation comparison

I am currently using ADuM4160 by Analog Devices as a USB isolator. However, this part is EXPENSIVE. I was wondering if anyone thinks it can be replaced with ADuM2200. Any reason why this wouldn't ...
4
votes
3answers
405 views

Why are the pins on the official arduino motor shield so long?

Here is the Official Motor sheild website. The shield has pin connectors at the bottom that are 2x longer than on any other shield I've seen. Why is that?
12
votes
3answers
3k views

Cellphone charger has no transformer?

I opened up a really tiny mobile phone charger I have, to see how it is designed. The entire "charger" is integrated into a small 2-pin mains plug, 1 x 1.25 x 0.5 inch, that has an USB socket for the ...
5
votes
1answer
431 views

Determining if a power supply is isolated?

I've been looking for a low cost adapter I can use to power some electronic circuits I'm playing with. Pretty much the only requirement I have at this time is that the adapter is mains isolated for my ...
3
votes
4answers
566 views

Measuring voltage while maintaining isolation

I'm building a variable power supply, and want to provide the ability to digitally measure the outputted voltage and current. The digital power supply used to drive the ADC, microcontroller and ...
6
votes
4answers
2k views

how to electrically isolate a PCB from a heat sink

I have a set of LED driving lights on my motorcycle that must be wired through a ground-leg pulse width modulation dimmer. The problem is the mounting bracket for the lights is grounded, so the lamp ...
0
votes
2answers
242 views

How to implement an isolated connection matrix

I need to implement a circuit for a researcher, which looks a little bit like this: Description of the circuit: There are two or more fully isolated biphasic current drivers, and N output pins. ...
1
vote
2answers
442 views

Isolation transformer weirdness

I recently posted a question about cutting the ground wire in an isolation transformer to make it truly isolated. After reading the responses, I decided the best advice was to reconnect the ground ...
5
votes
3answers
1k views

Cutting the ground wire in an isolation transformer?

I bought a non-tech isolation transformer (500w), which I planned to cut the earth mains ground from the output, but leave the chassis grounded; however, when I opened it up I found the output outlets ...
4
votes
3answers
1k views

home brew isolated oscilloscope lead

The ground clip for an oscilloscope lead is normally connected within the instrument to the power supply earth, and there are surprising circumstances where this could matter. The situation is very ...
11
votes
2answers
6k views

What values of resistor and capacitor to use for AVR reset pin isolation?

Background... I'm a newbie to AVR applications. I recently built two ATTINY13-based circuits (glorified LED blinkers) which worked correctly (independently) on the breadboard. When I combined them on ...
5
votes
1answer
755 views

How should I isolate AC and DC on a small PCB?

I am designing a small PCB (1"x1") and it will have some DC logic traces (5V and GND) and some high frequency AC power traces (100V 1000Hz 50mA). Are there any special considerations I need to take ...
1
vote
1answer
542 views

How close can I place two transformers?

I need to place two of these transformers in a case. How close am I allowed to place them? Can they touch each other (of course, they will be electrically isolated)? Is their orientation with ...
5
votes
2answers
1k views

Isolation transformer and scope when troubleshooting SMPS

I have a simple question, when troubleshooting a SMPS is highly adviced to use an Isolation transformer. But my question is this, if im using a scope to troubleshoot the "hot" side of my SMPS, both ...
5
votes
1answer
4k views

Is galvanic isolation of Hi-speed USB impossible?

I have a USB isolator which provides galvanic isolation of a USB device from my PC, but only works for low speed and full speed USB. I can't find any alternative electric isolators which do provide ...
4
votes
1answer
154 views

how to test isolation of DCDC convertor?

I have an isolated DC-DC convertor which boasts a 1.5kV isolation. I have a PCB made along with the additional components it requires. How can I test it?
0
votes
2answers
487 views

Sixteen 100v isolated power supplies

I need to create sixteen isolated power supplies on a single PCB. Input voltage 9v DC. Output voltage 100v DC. Output current 10mA each. No precise regulation needed. Efficiency not terribly ...
3
votes
3answers
331 views

Isolation of watch crystal from ICSP

I'm working on a project which uses a PIC with a 32kHz watch crystal attached to Timer1. Unfortunately, the chip I'm currently using, PIC16F1827, shares the T1OSI & T1OSO pins with ICSPCLK & ...
7
votes
2answers
371 views

Isolation transformer to reduce speaker pop

I have some computer speakers which suffer from the following problem: when switches flip in certain devices in the house, like the thermostat on a radiator or the refrigerator, the speakers will emit ...
9
votes
1answer
1k views

Why does TO-220 79xx voltage regulators conduct the input voltage to the heat sink?

I find it somewhat dangerous to connect a large heat sink on 79xx series voltage regulators. Because they transfer all the negative voltage to the heat sink. Why just they didn't make the 2nd pin of ...
24
votes
4answers
5k views

Why are the high voltage overhead power lines with the same potential being isolated?

Photo #1 Photo #2 Photo #3 - A zoom of Photo #1 Photo #4 - A zoom of Photo #2 I shot these photos while travelling in a highway. In each line-group has three separate lines. I think that the ...
1
vote
3answers
270 views

How to hook up an FPGA to a component that has a different power supply?

I recently programmed my FPGA with a logic analyzer core for the purpose of reverse engineering a crappy modem I have. I found on it what I think is either JTAG or TTL-serial pads. There are 4 blank ...
8
votes
4answers
1k views

Sensing DC motor current

I am allowing the current through a DC motor to flow through a small resistor and measuring the voltage across it. I need to give this analog Voltage to an ADC of micro-controller to do some signal ...
3
votes
3answers
327 views

Sensing signal on a power line from high side

I have a circuit design as above. I'm trying to sense the voltage difference accross the \$ 0.1 \Omega \$ resistor. I physically connected the sensory circuit to the low side of the AC line, and saw ...
6
votes
2answers
1k views

Isolation Transformer

When a function generator is used to power a full wave rectifier an oscilloscope will not show the correct output due to a shared ground. A half wave is displayed because one of the diodes is ...
1
vote
1answer
267 views

Isolating BNC connector from test shield

For my project, I need to have BNC connectors on the test metal shield. So what I did so far is drilling holes, and mounting BNC connectors on it: I used some hot shring on the part which passes ...
5
votes
1answer
308 views

How is pouring water addressed in high-voltage electric transport systems?

An electric train is typically powered with something like 1.5 kilovolts of direct current of something like 25 kilovolts of alternating current. In my experience electric device manufacturers charge ...
0
votes
3answers
2k views

How to make two isolated power sources from one source?

I need to have two electrically isolated power sources. Here are the details of the application: http://revolectrix.fmadirect.com/support_docs/item_1377.pdf page 26: I need to make this work with ...
0
votes
0answers
362 views

Is this buffer for protecting 3.3v logic from 9v power sane?

I'm playing with the idea of making a multi-interface for classic game controllers. The interface connector between the system and the controller has several pins that can be used bidirectionally ...
1
vote
1answer
216 views

Augment battery-run device power with 100mA solar cell?

I may be running a microcontroller for an extended period of time in a portable manner under battery, but do not want its life to be reduced by a silly load such as an LCD screen (5v + backlight) ...
1
vote
1answer
790 views

Need to isolate my ammeter (measuering and powering the unit from same power source)

I have a problem and Im not sure what the best way is to address this. I converted an ATX PC power supply to use as a lab power supply I installed a digital volt meter and a digital ammeter. To power ...
3
votes
2answers
306 views

How to properly isolate multiple power supplies

Say you have a single 110V AC supply and need to use it for a number of devices, each requiring very different characterists. For me personally these are: a direct use of the 110V AC supply for a ...
1
vote
2answers
487 views

what would be the most suitable components to replace some relays?

I'm working on an electronic product based on a microcontroller that must be able to control a series of actuators: 230V AC motors ON/OFF, 24V DC motors ON/OFF, 80V/20A heating element ON/OFF. The ...
4
votes
2answers
391 views

Electrical Isolation

I've been reading about the EIA-485 standard and they talk about how even with twisted pair wire they need a 3rd connection for common because sometimes the devices need to be isolated. I was thinking ...
5
votes
3answers
1k views

Why is power supply from electrical utility referenced to earth?

In response to the question Basic Training for working with 120V AC zebonaut had replied that "A regular wall outlet is referenced to earth" and this provides the close loop for the circuit to ...