Any way to use a mere 2.6 volts to trigger larger voltage switching?

[tomzarbo]

I worded that question kind of strangely, but here is what I'm trying to do...

This thread: Two New Radio Faceplate Preamps... - Techtalk Speaker Building, Audio, Video Discussion Forum (parts-express.com)

describes a fairly decent little faceplate preamp that I'd like to use for my next radio project.



I tapped into every solder joint I could find and the only thing I find that switched on/off with the unit is the 2.6 volts that powers the screen backlight LED's (this is to trigger a time delay relay to turn on the amplifier a few seconds after the preamp unit)

I was hoping the USB would be switched as it is 5v and would work perfectly with the 5 volt time delay relay board I already have, but alas... it stays powered up even when the unit is off.

If I just throw a switch to turn on everything, it will erase the FM presets so I'd rather not do that.

My goal is to just have to turn on the preamp, and have it trigger something to turn on the amplifier.

So any ideas how I could use 2.6 volts (at probably fairly low amperage capability) to trigger another switching device? Some type of transistor circuit (easy hopefully) to trigger one of the time delay relay devices? That's above my knowledge base at this point.

Thanks for any ideas. Otherwise, I'm going to have to do what I've always done... have the preamp turn on/off by itself, and use a switch to turn on/off the amplifier section separately. Not the end of the world, but I'd love to move past this obvious band-aid if possible.

TomZ

[tom_s]

Tom - you can find little low voltage boost boards on Bezos' site. If you have Prime, they should be there in just a few days. Seems QC is lacking for many of these devices, but they usually come in quantities of 5 or more, so getting one good one for your project shouldn't be too tough. You'll find one with adjustable output if you Google Eiechip dc to dc Step up

[DeZZar]

How about using a transistor? Here is something I found online. http://www.wam.umd.edu/~toh/ElectroSim/relay.html

And some information on using transistors as switches: https://www.nutsvolts.com/?/magazine...may2015_Secura

[tomzarbo]

Tom - you can find little low voltage boost boards on Bezos' site. If you have Prime, they should be there in just a few days. Seems QC is lacking for many of these devices, but they usually come in quantities of 5 or more, so getting one good one for your project shouldn't be too tough. You'll find one with adjustable output if you Google Eiechip dc to dc Step up

Thank you Tom.
I don't often have much luck searching for things like this. I ordered a batch of them and I'll play with them a bit and see if they will do the deed for what I need.

How about using a transistor? Here is something I found online. http://www.wam.umd.edu/~toh/ElectroSim/relay.html

And some information on using transistors as switches: https://www.nutsvolts.com/?/magazine...may2015_Secura

Thanks DeZZar, I read the articles, but need to read them again so it soaks in better. That was interesting. I'll look at that again this weekend when my mind is more clear.

Thanks guys for the guidance. I appreciate it, and I'll keep you posted on how it turns out. I think it's important to document this stuff as it will help others in the future. Heck, it will probably help ME in the future as I tend to forget stuff after a few years of non-use.

By the way, I know of a way to get all the features I want, (or at least most) in a table radio preamp... it's called a car stereo... retained power, power antenna/remote amp turn-on... decent FM reception... I've put a few of them through their paces already, but they are just too wide/and or tall for a small radio. That's why I'm using this type of preamp... the next radio I work on will be petite, and a car stereo -- even single DIN -- would just be too big.

TomZ

[tomzarbo]

Well, I tried at least... I had hoped this would work, but it's just not in the cards I guess.

I used one of the voltage booster boards (upper left) that TomS mentioned and the unit did work, as in it boosted the voltage to 5 volts, and even up over 20+ with some screw twiddling, but the preamp board just doesn't output enough amperage to get this setup working correctly.

I tapped into the only switched voltage I could find on the board and it was 2.6 volts to turn on the display LED backlight. When I connected the little voltage booster board the screen got considerably dimmer, even though the booster board is very efficient. It would provide only a bit over 3 volts to the 'delay relay' board no matter how I adjusted the booster board. It would cause the LED on the relay board to light, but there wasn't enough amperage/voltage to trip the relay. I think the preamp just isn't supplying enough power to the backlight circuit to do anything else but run that.... I can't fault that design, it works as intended.

I just wish the people that designed these little preamp board would THINK a bit! It needs an amp to do ANYTHING, why not allow for onboard switching of the amp board? Oh, how I wish PE would build a nice Dayton-version of one of these things... Maybe I'll write PE another email on that.

So... I'm going back to the manual switch for the amplifier circuit only and using the preamp as is. I don't want to build a circuit to try and remedy this, I've spent too much time fiddling with it already, and I'm getting frustrated a little at my lack of progress, so... forward I march!

I do have a few nice switches to use for this, backlit ones with nice action to them, so it's no big deal really.

Thanks for the input on ideas for this. I'll post up about the radio once I get it rolling sufficiently.

TomZ

[davidB]

How about a removeable faceplate head unit.

Just take off the mounting plate and set it into the panel wherever you want.

[tomzarbo]

How about a removeable faceplate head unit.

Just take off the mounting plate and set it into the panel wherever you want.

You're speaking of a car stereo unit? Yeah, that would be a good option for some table radios, and I've tested out a few for this exact purpose. One of them was less than 3" in depth, which is really thin enough to fit pretty much in any situation.

...But this radio will be very modestly sized and a car stereo single DIN is even too wide to work. This unit is nearly half the width and just makes the front width much more compact looking. Good idea, though. And car stereo head units have most of the stuff that these preamp boards lack, like a remote-on lead, and excellent FM reception. Not to mention decent sized volume knobs (some of them). Thanks for the input.

TomZ

[dali]

Maybe a little late but maybe you could use an optoisolator til 111 ic and use the 5v of the usb to switch the relais?

[tomzarbo]

I'm just wondering if anyone has anything like I'm trying to do specifically. I did finish up the radio and it works fine, here is a link: https://techtalk.parts-express.com/f...1-sound-system Video here: https://www.youtube.com/watch?v=TJxKuKbibXs

I would just love to be able to have a fairly solid way of stealing a little voltage from these little preamp boards to power-on an amp. I've made a dozen of these things by now if I've made one, and they all have needed their own switch for the amp... I just don't understand how these goofy manufacturers keep missing the boat with this... I'm about to give up and just go with car radios... I've gotten a few of those ready to use as well, but they're a bit big, or wide if you're looking for a really small table radio.

Anyway. I'm hoping there is a fairly easy way to do this... and it doesn't have to be just 2.6 volts, probably a range would be more flexible... maybe 2.5 to 5 volts, something like that... but since it will probably be low amperage as it's robbed from the preamp board it has to be... it just needs to switch a 5 or 12 volt time delay relay board... or if it's a solid state relay, I guess it could switch it directly.

Trouble is, I'm having a hard time navigating the specs on Mouser and Digikey to find a solid state relay that will switch on/off with as little as 2.5 volts but still switch on something with decent amperage.

Let me boil it down... I have 2.5 volts to 5 volts switched on a preamp board for a table radio. I need to get that low voltage with miniscule amperage to switch, trigger, activate... whatever you call it... something that can act as a switch to allow an amplifier to be powered up. NONE of these goofy preamp boards have a way to do that for some goofy reason. Can you tell I'm a bit miffed? (Hint: I used the word goofy three times in this post)

I looked into all the suggestions posed here, and thank you, but I'm having a bit of trouble putting it into a workable action plan. I'm hoping someone has experience and may be able to point me to the parts I'd need to pull this off.

Thank you,

TomZ

[wogg]

Hey Tom, I think a solid state relay is what you're looking for. I used one for the remote turn on in my Indy 8 powered setup. They will switch any higher voltage / power signal with the input looking like a simple diode junction. Give the diode enough current, the relay closes. The diode is an LED and needs just over 1V to work, you just calculate the resistance needed to give it the current needed to kick on with whatever input voltage. For the Indy 8, I gave it a resistor to work with an input voltage range from 5V to 12V so I could use a USB port or a 12V switching voltage from any device.

Sadly, I can't find my order information for the specific part number I used, that was a bit outside the range that DigiKey keeps order history. It looks like it may have been a Panasonic PhotoMOS™ AQZ series device though, like the AQZ102. They're not super cheap at about $20 when bought single.

To get the resistance, you need some classic Ohm's law. The datasheet says 1.25V forward voltage, and between 1 and 3 mA to turn on with 30mA maximum. So with your 2.5V input you'll calculate resistance like this:
2.5V in - 1.5V LED forward voltage = 1V across your resistor. Let's target 5mA for on current, so Ohms' law says 1V / 5mA = 200 Ohms. At 200 Ohms, you'll want to know your max voltage before damaging that $20 relay, which will be 200 Ohms * 30mA = 6V. You'll be able to turn on any DC voltage with that AQZ102 up to 60V and 4A with an input voltage from 2.5 to 5V safely.

[3rutu5]

Got any tips for my 12v beer can and a tiny relay? My design flaw was the on off volume pot doesn't switch off the amp/BT it would seem and the power stays on. So was curious if something powering up for turn it on or off...why not just wire an on off switch? Because I've 3d printed, primes and painted and found out the battery drains once it was finished lol

[wogg]

A couple issues will prohibit that particular relay: they're too big and expensive. They do have small 8 pin DIP relays that may work, or it would take some EE design work to use discreet mosfets to switch. Either way your into some design work and small PCB creation.

[tomzarbo]

Hey Tom, I think a solid state relay is what you're looking for. I used one for the remote turn on in my Indy 8 powered setup. They will switch any higher voltage / power signal with the input looking like a simple diode junction. Give the diode enough current, the relay closes. The diode is an LED and needs just over 1V to work, you just calculate the resistance needed to give it the current needed to kick on with whatever input voltage. For the Indy 8, I gave it a resistor to work with an input voltage range from 5V to 12V so I could use a USB port or a 12V switching voltage from any device.

Sadly, I can't find my order information for the specific part number I used, that was a bit outside the range that DigiKey keeps order history. It looks like it may have been a Panasonic PhotoMOS™ AQZ series device though, like the AQZ102. They're not super cheap at about $20 when bought single.

To get the resistance, you need some classic Ohm's law. The datasheet says 1.25V forward voltage, and between 1 and 3 mA to turn on with 30mA maximum. So with your 2.5V input you'll calculate resistance like this:
2.5V in - 1.5V LED forward voltage = 1V across your resistor. Let's target 5mA for on current, so Ohms' law says 1V / 5mA = 200 Ohms. At 200 Ohms, you'll want to know your max voltage before damaging that $20 relay, which will be 200 Ohms * 30mA = 6V. You'll be able to turn on any DC voltage with that AQZ102 up to 60V and 4A with an input voltage from 2.5 to 5V safely.

Thank you wogg, for that input,

After my coffee starts to kick in, I'll check out that concept. The $20 price may be prohibitive to doing this, but I'll try and understand the concept you outlined anyway so I can sort of know what options there are. I wish I had gotten into this stuff when I was younger and sharper so I could understand it a bit easier, but it's still kind of fun to learn new ways to make electrons do what you want.

Thanks sir!

TomZ

[tomzarbo]

I looked into the relay you mentioned Wogg, I think I understand most of what's going on.

TomZ

[wogg]

I looked into the relay you mentioned Wogg, I think I understand most of what's going on.

TomZ

Cool! That little bugger was one of the more expensive parts in that cheap build, but I wanted input voltage flexibility and no clicky mechanical relays... so there was that.

[tom_s]

Hey Tom - this is a little late, but I think you could easily do this with an Arduino Nano clone and a small relay. The Arduinos input pins don't draw much current - I'm told it's in the uA range. Sadly, the prices have tripled with all the disruptions in the supply chain. You used to pay $12 for 3 of the Chinese clone boards, but right now that's the going rate for just one. If I had any spares, I would send you one to play with, but I think mine are all in use right now.