Help on DTMF output Latch / Momentary??????

Dear All,
I have DTMF decoder IC MT8870 for my Remote control Relay project.
(1) I want to know, Whether MT8870 have a LATCHED output or Momentary??
(2) In my project MT8870 shows latch output (Continuously High when pressed)
(3) Is there and provision to make is momentary as I want to on/off relay/LED connected to its output.
It will be of great help if you reply urgently
Regards,
T.D.

The data outputs ARE latched, they stay set even after the input tones are removed.
The strobe output is momentary and only present when a valid DTMF signal is being decoded.
If you want the output to be present only when a tone is heard, you need to logic AND the latch outputs with the strobe signal.

Brian.

betwixt said:

The data outputs ARE latched, they stay set even after the input tones are removed.
The strobe output is momentary and only present when a valid DTMF signal is being decoded.
If you want the output to be present only when a tone is heard, you need to logic AND the latch outputs with the strobe signal.

Brian.

Click to expand...

Dear Mr.Brain,

Thank you very much for your above reply.

As per your explanation I have checked and confirmed followings,

(1)Q11-to-Q14 BCD outputs are LATCHED when valid tone decoded. And stay high until next tone /BCD code recived.

(2)Std (Pin no.15 of MT8870) high Momentary when valid tone received/decoded.

Now I am facing following problem,

(1)
I have connected D flip-flop (IC 4013) at one of the output (say pin no.11) of MT8870 to CLK of (IC 4013). But as the BCD output of MT8870 (pin no.11) is continuously high and doesn’t change its state when same key is pressed simultaneously to turn on/off appliances, as a result CD 4013 output also gets unchanged.

In other word, when the same key (suppose 1 from DTMF tone generator) pressed (to turn on the appliance) CD 4013 output LED glows and again pressed to turn off the appliances D- flip-flop doesn’t change its state. (as the BCD code in both cases is 0001 keeping CLK high only). REQUEST TO PROVIDE PROPER SOLUTION.

(2)
When I switch on the power of the DTMF receiver circuit(IC MT8870), a random output at LEDs (connected at BCD output of MT8870) glows. Hence I guess, if I connect relay to control appliances gets on randomly when circuit powered on.
Below find sketch of circuit for better understanding.

View attachment Remote Control.bmpKindly help me out… plzzz..

And also provide if you are having any simple 4 Channel Output Electrical Appliance Control Circuit.

Ones again thanks for your quick help……

Awaiting for your reply….

Regards,
T.D.

Instead of using D-flipflop why dont you use a simple nand gate with one output from std(pin15) and another from bcd.

With a single chip you can connect all the four bcd outputs

nandhu015 said:

Instead of using D-flipflop why dont you use a simple nand gate with one output from std(pin15) and another from bcd.

With a single chip you can connect all the four bcd outputs

Click to expand...

Dear Mr. Nandhu,

As per your suggestion I will try it out and come to you with result…

Meanwhile, one doubt striking in my mind by using AND gate, request you to plz clarify,

(1) If I connect AND gate with Pin-15 and BCD output pin no.11 to AND gate.

Now, in above case-1;
A. When I press 1(to switch on the appliance-1) on DTMF tone generator. Than same is received at MT 8870 and decoded as 0001, which drives the AND gate output high and ultimately glowing of LED / Relay.

B. Now, if I press 2 (to switch on the appliance-2) on DTMF tone generator. Than same is received at MT 8870 and decoded as 0010. Now in this case my AND gate output which is at high state will change or not???

Now, in above case-2;
A. When I press 1 (to switch on the appliance-1) on DTMF tone generator. Than same is received at MT 8870 and decoded as 0001, which drives the AND gate output high and ultimately glowing of LED / Relay.

B. Now, if I press 1 again (to switch off the appliance-1) on DTMF tone generator. Than same is received at MT 8870 and decoded same as 0001. Now in this case my AND gate output which is at high state will change or not??? (Ideally to control appliance, it should change/alter its state each time when same key is pressed on DTMF tone generator.)

Sketch of the circuit based on your reply attached for better understandin.
View attachment MT8870 with AND Gate.bmp.

Looking forward to hearing from you…

Once again thanks for your response…..

Regards,
T.D.

I think you misunderstood my option.

I'll try to make it clear.
You have to use four nand gates for each bcd output.
All the first inputs of four nand gates should be connected to pin15 and
the other inputs should be connected to bcd output's respectively (i.e. first bcd output of mt8870 to the input of 1st nand gate and so on..)

Hope this is clear

nandhu015 said:

I think you misunderstood my option.

I'll try to make it clear.
You have to use four nand gates for each bcd output.
All the first inputs of four nand gates should be connected to pin15 and
the other inputs should be connected to bcd output's respectively (i.e. first bcd output of mt8870 to the input of 1st nand gate and so on..)

Hope this is clear

Click to expand...

Dear Mr. Nandhu,

Based on your suggestion I had prepared a sketch of the circuit with NAND Gate.

And also prepared a Truth table for circuit, both are attached here.
View attachment MT8870 with NAND Gate.bmpView attachment MT 8870 Truth Table.bmp

Referring to this, I think when I press Switch-1 on DTMF generator to switch “ON” the appliance-1 which is connected to MT8870 output Q11 through NAND-1 gate.

It will instead of Switching “ON” the appliance-1, pull down the output of NAND-1Gate to Zero(0). Which in turn switch off the appliance-1 and switch on all rest appliances -2,3,4.

As I want to drive the Relays through the transistor (BC 548) to switch ON/OFF the appliances-1,2,3,4.

I think there we want LATCH output (when “ON” command received) which in turn picked up the relay till the switch “OFF” Command detected.

Waiting for your valuable reply…

Regards,
T.D.

If I understand, you want one DTMF code to be a universal "OFF" command to all appliances and all the other codes to be "ON" to one of potentially 15 appliances. I say 15 because there are 16 different combinations of output in total.

If I am right, you also need a decoder to expand the four binary outputs to more lines. You can not control 4 appliances with three bits and a reset without additional decoding. I strongly advise you to look at using a microcontroller to do the extra things you need. The software is very easy and you will use fewer components. Although the application is quite different, look at ATV-Projects DTMF Control Unit to see how I did it to control 8 devices with a simple circuit.

Brian.

betwixt said:

If I understand, you want one DTMF code to be a universal "OFF" command to all appliances and all the other codes to be "ON" to one of potentially 15 appliances. I say 15 because there are 16 different combinations of output in total.

If I am right, you also need a decoder to expand the four binary outputs to more lines. You can not control 4 appliances with three bits and a reset without additional decoding. I strongly advise you to look at using a microcontroller to do the extra things you need. The software is very easy and you will use fewer components. Although the application is quite different, look at ATV-Projects DTMF Control Unit to see how I did it to control 8 devices with a simple circuit.

Brian.

Click to expand...

Dear Mr.Brian,

I think it will more clear if I attach a circuit on which I’m working. The same is attached here.

View attachment DTMF Remote Relay Control Circuit.pdf

With reference to circuit, you will find MT8870’s BCD output (Q11-14) is connected to IC 4013(D flip flop in toggle mode).

Now, as the BCD output of MT8870 is latched (Continuous high), connected toggle flip-flop could not change its state when same key is pressed once to switch “ON” and again to Switch “OFF” the relay/appliances connected to it.

Request you to provide suitable solution.

Awaiting your valuable reply..

Regards,
T.D.