Control two circuits with one switch  - Page 1
Forum section: electronics / beginners

author: 24ariel3
author_rank: Contributor
timestamp: October 24, 2018, 02:57:32 pm
content: Hi,I've two simple circuits with different voltage levels something like this:Basically what I want is to be able to control both leds with the switch on the right while the switch in the left will work undisturbed if the switch on the right is 'open'.How can I make it work that way?Thank you!

author: Mattjd
author_rank: Regular Contributor
timestamp: October 24, 2018, 03:15:39 pm
content: Use a mosfet to switch the leds and control the mosfet with a switch

author: pix3l
author_rank: Regular Contributor
timestamp: October 24, 2018, 03:17:54 pm
content: Or use a DPDT switch on the left side and a normal switch on the right side

author: 24ariel3
author_rank: Contributor
timestamp: October 24, 2018, 03:35:08 pm
content: I'm a noob where exactly should I put the mosfet?

author: Karlo_Moharic
author_rank: Regular Contributor
timestamp: October 26, 2018, 05:56:33 pm
content: Schematic that you have attached , shows two circuits with SAME voltage levels.

author: 24ariel3
author_rank: Contributor
timestamp: October 26, 2018, 07:29:38 pm
content: Quote from: Karlo_Moharic on October 26, 2018, 05:56:33 pmUploaded a new image with different voltage levels

author: Brumby
author_rank: Unknown
timestamp: October 26, 2018, 10:18:41 pm
content: Quote from: pix3l on October 24, 2018, 03:17:54 pmI like that idea, but it doesn't need a DPDT. A DPST would do and I'd put it on the right - each side controlling one circuit. The single pole switch goes in the left side.Can you join the negatives of each circuit? If so, this would make it a simple logic problem where a single diode could do the job.

author: Karlo_Moharic
author_rank: Regular Contributor
timestamp: October 27, 2018, 07:01:41 am
content: Given your specs , what I would recommend is a Double Pole , Single Throw (DPST) switch on the right and a Single Pole Single Throw (SPST) switch on the left.here is a link to explain different switch types:https://www.efxkits.com/blog/types-of-switches-with-applications/

author: 24ariel3
author_rank: Contributor
timestamp: October 27, 2018, 09:29:04 am
content: Quote from: Brumby on October 26, 2018, 10:18:41 pmLet's assume the two are completely separate devices and need to remain isolated devices so we cannot join the negatives.Quote from: Karlo_Moharic on October 27, 2018, 07:01:41 amDPST can be a nice solution but let also assume that we cannot change the existing hardware, we can only add components on the existing hardware, for example the first one is a TV remote controller and the second is an A/C remote controller and we want to be able to turn both on by pressing 'on' button on the TV remote controller.The way I see it is something like that:

author: Karlo_Moharic
author_rank: Regular Contributor
timestamp: October 27, 2018, 12:08:09 pm
content: OK , wait a minute , your original question was about 2 simple LED circuits.Now you are saying you have TV & A/C and you would like to turn them both on by using only TV remote.That is enterely different type of problem you are trying to solve.If the issue is that you wish to add extra functionality to your TV remote , then you just need arduino & IR sensor for arduino.But before I explain that , did you consider using either remote control outlets or universal remote (one of those 6in1 that support whole range of devices at the same time) ?Now regarding arduino , what you do first is you write simple IR receiver program and you simply record both "ON" signals from TV & A/C remote. Now once you have those , arduino simply works as a translator. What you do is you simply put arduino parallel to IR receiver inside A/C unit and when ever it's IR diode sees "ON" signal from TV remote , you simply tell it to send a proper "ON" signal to A/C IR receiver. You can also use this method to completely take control of A/C unit with TV remote , simply by recording codes from your A/C remote.

author: 24ariel3
author_rank: Contributor
timestamp: October 27, 2018, 12:58:15 pm
content: well the remote controller was only an example my question is a general one assume we have two different systems is it possible to control one of the systems by controlling the other system.Another example can be controlling a BT receiver from car's stereo system, pressing 'next' on the stereo system will 'press' next on the BT receiver and will skip a song.Microcontroller/arduino may be needed but I'm not sure yet how to it

author: Karlo_Moharic
author_rank: Regular Contributor
timestamp: October 27, 2018, 01:11:04 pm
content: Quote from: 24ariel3 on October 27, 2018, 12:58:15 pmIn that case your question is too general to be given a specific answer.

author: 24ariel3
author_rank: Contributor
timestamp: October 27, 2018, 01:24:33 pm
content: Quote from: Karlo_Moharic on October 27, 2018, 01:11:04 pmOk. let's focus on my last example it is closer to my actual problem.can we control a BT receiver from car's stereo system, pressing 'next' on the stereo system will 'press' next on the BT receiver and will skip a song.

author: Karlo_Moharic
author_rank: Regular Contributor
timestamp: October 27, 2018, 05:00:21 pm
content: Give me the exact model & make of both your car radio and BT receiver.

author: spec
author_rank: Frequent Contributor
timestamp: October 27, 2018, 09:49:21 pm
content: + 24ariel3Part of your schematic from reply #8 is reproduced below. When SW2 is open would a current, Iq, of 100uA be acceptable?

author: 24ariel3
author_rank: Contributor
timestamp: October 27, 2018, 10:10:25 pm
content: Quote from: spec on October 27, 2018, 09:49:21 pmI think it should be fine, what is on your mind?

author: spec
author_rank: Frequent Contributor
timestamp: October 28, 2018, 04:40:37 am
content: Quote from: 24ariel3 on October 27, 2018, 10:10:25 pmThat's good newsI will post a schematic and an explanation for you. Both battery circuits will be completely isolated.

author: spec
author_rank: Frequent Contributor
timestamp: October 28, 2018, 11:53:30 am
content: As promised, a schematic for your 'Something' is attached. Here is an explanation of how the circuit works:Two slightly unusual components are central to the design: depletion mode NMOSFET, photovoltaic (PV) coupler.Most NMOSFETS are enhancement mode types so that when the voltage between their gate and source (VGS) is zero the resistance between their drain and source (RDS) is very high. To make an enhancement mode NMOSFET conduct the gate needs to be made more positive than the source.But, in contrast, depletion mode MOSFETs have a low resistance between their drain and source when the voltage between their gate and source is zero. So depletion mode MOSFETs are rather like thermionic valves in this respect. To turn a depletion mode NMOSFET off the gate must be made more negative than the source.PV couplers, unlike the more common opto couplers, produce an output voltage when current flows through their input LED. The output is only capable of sourcing a low current though. Like the opto coupler, there is complete isolation between the input and output.The circuit works as you say in reply #18 (posted before this post was complete).The truth table is:SW2SW1LED2LED1OpenOpenOffOffOpenClosedOffOnClosedOpenOnOnClosedClosedOnOnHere are some points about the design:You may be wondering, why two PV couplers. The reason is to get sufficient negative voltage to turn the depletion mode NMOSFET off (-2.1 VGS) and have an Iq of 100uA, which I thought would be a reasonably low current. But if an Iq of 200uA were acceptable, by changing R3 to 33K, you could use just one PV coupler.R5, C1, and, C2 have no role in the general functioning of the circuit.R5 is a gate stopper which is a precaution to discourage the NMOSFET from oscillating. R5 should have short leads and be connected directly to the NMOSFET gate terminal.Likewise C1 should have short leads and be connected directly between the MOSFET drain and source.C2 also helps the stability of the NMOSFET, but is is mainly for smoothing the voltage from the PV couplers.C1 and C2 should be high frequency low ESR capacitors, ceramic X7R dielectic or metal film polypropylene. The values of C1 and C2 are not critical.This is a paper design, so it has not been built and tested. If you build the circuit I hope it works OK.Data Sheets:NMOSFET DN2625http://ww1.microchip.com/downloads/en/DeviceDoc/20005537B.pdfPV Coupler TLP3905https://toshiba.semicon-storage.com/eu/product/opto/photocoupler/detail.TLP3905.html

author: 24ariel3
author_rank: Contributor
timestamp: October 28, 2018, 03:08:58 pm
content: OK so let's see if I got itphotovoltaic coupler when S2 is open current flows through N2 and N1 leds which means they are turned on and the photovoltaic 'cells' inside them are generating enough voltage to keep the depletion mode NMOSFET open and when S2 is closed the depletion mode NMOSFET is closed too which means both leds are now turned on.Am I correct?

author: spec
author_rank: Frequent Contributor
timestamp: October 29, 2018, 03:39:30 am
content: Quote from: 24ariel3 on October 28, 2018, 03:08:58 pmYes, that is a good summary of the circuit's overall function.Update 2018_10_30: Just to let you know answer #17 is now complete.

author: Mattjd
author_rank: Regular Contributor
timestamp: October 31, 2018, 12:31:42 am
content: Quote from: pix3l on October 24, 2018, 03:17:54 pmyes thats vastly easier. My lack of practical applications, I forget there are all the different types of switches.

author: spec
author_rank: Frequent Contributor
timestamp: October 31, 2018, 02:41:03 am
content: Quote from: Mattjd on October 31, 2018, 12:31:42 amAgree, but it does not meet the OP's requirements.