volume attenuator relay

Thread Starter

arivel

Joined Mar 4, 2018
19
Hello.
I would like to make a volume attenuator composed of bistable single coil latch relays in logarithmic resistor ladder configuration.
to do this I thought of using a binary counter 40193 whose outputs go to an operational amplifier. the function of the operational amplifier is to send a pulse to the TC4420 half-bridge mosfet (attention, only one pulse at each change of state of the 40193) which controls the relay coil. to drive the bistable latch relays it is customary to use a pulse in one direction or the other without leaving the coil under voltage all the time.
as you can see from the attached image the other end of the coil is connected to the zero of the dual power supply.
to simplify, only one component of each type appears in the image (opamp, tc4420, relay), but in the real circuit there are at least six.
the problem is the following:
which op amp should i use? and which configuration is the most suitable?
 

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I would use a microcontroller in place of the 40193, the op-amps and pulse generators. An ATMEGA386 would be my first choice. What are you planning on using for an input?
I made one using low power, non-latching relays. It switches from 0db to -22.5db in 1.5 db steps. I control it with a TV style IR controller.
 

Thread Starter

arivel

Joined Mar 4, 2018
19
I would use a microcontroller in place of the 40193, the op-amps and pulse generators. An ATMEGA386 would be my first choice. What are you planning on using for an input?
I made one using low power, non-latching relays. It switches from 0db to -22.5db in 1.5 db steps. I control it with a TV style IR controller.
thank you for your answer but I am not able to program, I am of a certain age and I do not really want to start studying a programming language, plus I am fond of old electronics. by input you mean what controls the inputs of the 40193? .
there are two nand gates.
 

Ian0

Joined Aug 7, 2020
1,579
1) There are latching relays with two coils, pulse one for open and the other for closed, so you don't need a bridge driver of positive and negative supplies.
2) Latching relays are generally power relays, with silver oxide contacts, and they can make a real mess of the signal. If there is no substantial current flowing they start to behave like diodes. You must use relays with gold contacts, or reed relays which enclose the contacts inside a tube full of inert gas.
Signal relays are smaller with higher resistance coils, so there is no need for power saving and so the latching type tends not to be available.
 
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