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relay controlled potentiometer..

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wireman121

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I'm new to the custom circuit design game, but I understand the basics of what I need. Here is my situation:

I have an audio amplifier that takes a 10k pot connection to determine the volume it needs to amplify at. I need to be able to control this 10k pot with a 30v relay output signal (or it can be an IR signal, if I need to go that far.) I was able to find the Maxim MAX5457EEE+ chip which appears to do what I would need. I would need to drive a bunch of relays that will take a 30v input and convert it to a lower voltage that the MAX5457EEE+ will underatand. I would need to design a custom PCB as well. I dont know how to do that. I can solder no problem, but I've never designed my own complete circuit before.... any help with this would be much appreciated. I already have a bunch of MAX5457EEE+ chips, but I dont have any of the other components (nor do I know exactly what else I need to get) but I do have the system that will be sending the 30v signal (1 for volume up and 1 for volume down) I need to control 3 amps, so there will be 6 30v triggers as well as 3 seperate mute triggers for a total of 9 (so I will be using 3 MAX5457EEE+ chips)

Thanks!
 
Not clear what sort of control you want. Are you trying to get pre-defined volume settings? Why use relays? Transistor switches would be much easier.
 
Well the MAX5457EEE+ is a 10k pot that moves up or down depending on which pin gets voltage. I have a controller that will provide 3 seperate 30v "relay trigger" outputs when it needs the pot to move up, move down, or mute. I need the ability to take those outputs and drive the MAX5457EEE+ with them...
 
Here is a layout of what I'm looking to accomplish. The RTI module has the 30v outputs, which I will configure to send a momentary output when I need volume up, volume down, mute, or shutdown (latching)
I need help getting a CB printed that will allow me to attach components to it. I need to be able to convert that 30v (on the PCB) to something that the Max chip will accept without blowing up. I need to have spots for (and part numbers) of screw terminals like in the photo. Also, i can use an offboard power supply that will attach to the connector in the photo. Hopefully this explains what I'm looking to do a little better. I would need the PCB to house 3 of the max chips, and respective components to control a total of 3 seperate stereo volume controls (or 6 mono/bose amps)
**broken link removed**
 
If the voltage is a regulated 30V then you can just use a resistive 6:1 voltage divider to get the 5V for the pot control signal (for example 50K in series with 10k to ground). If it's not well regulated then you could use a 50k resistor in series with a 5.1V zener diode to ground.

Do you need a PCB because you are planning on building many of these? An relatively easy way to do PCBs is to use the free layout software from a supplier like ExpressPCB or PCB123. They sell small quantities of the finished PCBs for a reasonable price.
 
I'm thinking I need a PCB because the max chip only comes in a surface mount form. I'd also like to have it on a PCB to look professional. I would be using these from time to time on projects, but not a total mass production unless there was some sort of demand, which i doubt.

I kind of need help with the PCB design and which of the other components (voltage divider, etc) to use.... If someone would help me with that I could assemble it once it was here.... haha
 
the MAX5457EEE is a stereo volume controller that can be used to controll both left and right channels using push buttons so i dont understand why do u use it to control an ordinary pot? And what are u gonna do with a bunch of relays?
 
the Max5457EEE is a 10k audio taper pot, which is exactly what the Bose SA-3 amp VCA input is looking for. The relays were going to be between the RTI XP-6 and the Max5457EEE because the XP-6 outputs 30v for relay control and the Max5457EEE wont take 30v, so I needed to use something to step it down. Instead of pushbuttons, I am using the RTI XP-6....
 
the XP-6 outputs 30v for relay control and the Max5457EEE wont take 30v, so I needed to use something to step it down
A simple resistive divider will drop the volts down to suit the Max. Ditch the relays.
 
I dont know what a resistive divider is, nor do I know which one to use. I could really use some help with actual component numbers and maybe someone could help with, or lay out the PCB for me in ExpressPCB? I'm not planning on selling this or making money off of it at all, but I really could use the help as I need to be able to control these amps volumes through the RTI control.... I would be happy to pay for help if anyone requests it and can give me a PCB design along with part numbers? I know this isnt a hard project to build, but I just dont know enough about specific components to get the job done without wasting a ton of money on the wrong PCB design and components...
 
A resistive divider is just two resistors connected in series. See Carl's post #6.
 
Do you have 5V to power the MAX5457? If not then you need a regulator such as the 7805 to generate 5V from the 30V.

All you need to control the MAX is a transistor interface from the 30V.
For each PB input use any small NPN transistor (such as a 2N2222).
Connect each transistor collector to its respective PB input on the MAX
Connect the transistor emitters to ground.
Connect a 100k ohm resistor in series with each transistor base.
Connect each resistor to the appropriate 30V control voltage.
The 30V signal will now provide the same control as pushing the MAX control buttons would.

Is that all clear?
 
Yes, that all makes sense. To clarify, I dont have anything to power the MAX5457 right now. I was planning on using a 5v wall wart...the 30v is just the signal output, thats all.

1 last request - could you help me with a PCB design? I understand everything you said, but I've never designed a PCB before and I dont know if I'm doing it right or what all the correct components are......

I would need it to suppot using 4 of the MAX5457 chips (and the components needed to change the 30v signal to the correct signal for the 5457. I am planning on using screw terminals (suggestions?) for the input and output that would just accept cat5 gauged wire
 
A 5V wall-wart on its own will probably destroy the MAX, because wall-warts typically put out a much higher voltage than the rated value when they are lightly loaded. You will need to use a voltage regulator with a 5V output. Because of the light load you may get away with a '5V' wall-wart feeding the regulator (depending on both the wall-wart and regulator characteristics). Personally, I'd choose a higher-than-5V wall-wart.
 
If you use a wall-wart that has a regulated 5V output, then you should be okay. The small switching-converter type of wall-warts usually have a regulated output.

For the PCB design, I suggest you use a free PCB program such as from PCB123 or ExpressPCB. You are locked into buying the PCBs from them but their price is reasonable for small quantities. The software is fairly easy to learn. You draw the schematic and then it goes directly to the layout from that. Your board is not critical as to layout so you just place the parts to minimize the interconnect lengths. The PCB connections will automatically be shown as per the schematic.

For screw terminals you can buy terminal blocks designed for mounting on PCBs.
 
I'm trying to use ExpressPCB but I'm having problems figuring it out. Could you help me with a layout file, or should I create one and then upload it for checking? Not sure what would be easier...
 
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