Help please....

[carlandrewg]

Hi! can somebody please help me convert this circuit so that it can operate 12 relays? I don't know how to use the IC 74154 demultiplexer in the reciever circuit. My problem is with the reciever circuit only.. I want to make it a 12 output circuit instead of 4. Thank You!!!!!

 

[ClydeCrashKop]

Hook pins 11 – 14 to A,B,C &D of the 74154 (20-23) and a flip flop to each of the output pins, 1 – 11 & 13 – 17. (active low output) Then just send it a 4 bit number (0 – 15).
Pins 18 & 19 should be tied to ground. I like that circuit, I saved it.
Get a data sheet if you haven't.
That active low output will be a problem. You should stay with the CMOS chips because of that 4013 flip flop. Two 74C04 hex inverters maybe with pull up resistors after the 74C154 should do it.

 

[carlandrewg]

Thanks Clyde. But I cannot understand the last part. Do you mean I have to put a relay after each pin from pin 1 to pin 11 and then put another relay on pins 13 to 17? That would give me 16 outputs. I only want 12 outputs because the DTMF IC can only generate 12 frequencies. And how should I place the Hex inverters? Sorry for the many questions.. I'm just a newbie in electronics and I want to modify that circuit but I just don't know how. thak you very much!

 

[ClydeCrashKop]

You don’t have to use all 16. The flip flops toggle the relays on or off every time you address them. If you never need more than 1 relay on at a time then you don’t need the 4013 flip flops at all. The inverter just corrects the logic. On = High, V+ instead low, ground.

 

[Paul Obrien]

DTMF can generate 16 tones the A B C D are rarely seen or used, apart from that I concur with Clyde

 

[oldtimer]

I don't get it clyde,strapping the pins 11-14 to the abcd pins will hold the low on inputs less than 1100 would it be better just to leave them open. If you want to drive 12 relays a mosfet on each output 1-11 + 12 would operate each one as the inputs on ABCD increment. Just a question I have never used this chip.

 

[carlandrewg]

Thanks for the help guys! So I just need to strap pins 1 to 11 and pin 13 of the 74154 to 3 hex inverters so that I can generate 12 outputs? Thank you so much! Can't wait to try it.

 

[ClydeCrashKop]

I ass u me d that the RF chip can output a 4 bit positive logic number and that is what the 74154 wants as input on ABC&D. And that 74154 puts out active low negative logic which wouldn’t be right for flip flops or FETs so I think it needs to be inverted. I don’t know that chip either. We all know about assumptions. I hope I didn’t mislead.

You will need 2 hex iverters for 12 relays. (if I am right)

 

[ClydeCrashKop]

It seems that I didn’t read far enough about the 74154. It says in the description: Each 4-bit address drives one output low. All others stay high. Enable inputs E1 (18) & E2 (19) must be low. If one or both are high, all outputs go low. Down the page they show an example referring to pin 18 (E1) as DATA IN. With the description: Selected output is low when DATA IN is low. If DATA IN is high, selected output is high.
So, wire pin 18 high and forget the inverters. Also it looks like if you send it a 0000, pin 1, output #0 will be active. If you want all relays off when you send it a 0000, you should start with pin 2, output #1.

 

[carlandrewg]

Thank you Clyde. You were really helpful. So, I don't need the hex inverters anymore. I just strap pins 18 and 19 to VCC and then start my output relay on pin 2 instead on pin 1. Thank you very much for the help.

 

[ClydeCrashKop]

I thought maybe I had confused the issue so here is the latest version. Pin 19 still goes to ground.

 

[carlandrewg]

Thank You very much Clyde! You have been very very helpful!

 

[mostek]

Hi! can somebody please help me convert this circuit so that it can operate 12 relays? I don't know how to use the IC 74154 demultiplexer in the reciever circuit. My problem is with the reciever circuit only.. I want to make it a 12 output circuit instead of 4. Thank You!!!!!

Why dont you try a microcontroller after the dtmf decoder
it will make things easier