Hi,
I want to use my Kenwood TM-741 transceiver as an APRS transmitter in my
car. I plug my APRS system on Ignition 12v power, so it powers on
automatically when I start the engine.

The problem I have is with the TM-741: when 12v DC power is applied to it,
it doesn't power up automatically; i have to press on "power" button every
time. TM-741 CPU doesn't memorise power state when 12v power is cut.

Is there a modification or a programmation I could do to allow it to power
up automatically when 12v supply is applied to it? Any idea ?

Thank you in advance.

Daniel VE2BAP, Montreal, Canada

Hi Corkscrew,

Unfortunately, the 741 doesn't have a setting for "auto-power-on". My
first thought would be to add something that would parallel the power-on
button and perform the function you describe.

But be careful how you implement this: you can design a one-shot using a
555 or 74123 (I'm showing my age), but remember that when the power is
coming up, some devices' behavior may be unpredictable.

If I were designing something like that, I would do at least two things:
a) don't apply power to your circuit until it's been up for (say) 2
seconds, and b) if the 741 doesn't come to life (check backlighting
voltage, etc.) then re-cycle the power switch.

Another possibility, although primitive, would be to use a solenoid that
would physically press the power button, which wouldn't require
electrical modifications to the radio.

My two cents.....

73, good luck, and let us know what you do!

Dave
KZ1O


tirebouchon69 wrote:

Hi,
I want to use my Kenwood TM-741 transceiver as an APRS transmitter in my
car. I plug my APRS system on Ignition 12v power, so it powers on
automatically when I start the engine.

The problem I have is with the TM-741: when 12v DC power is applied to it,
it doesn't power up automatically; i have to press on "power" button every
time. TM-741 CPU doesn't memorise power state when 12v power is cut.

Is there a modification or a programmation I could do to allow it to power
up automatically when 12v supply is applied to it? Any idea ?

Thank you in advance.

Daniel VE2BAP, Montreal, Canada

Hi Corkscrew,

Unfortunately, the 741 doesn't have a setting for "auto-power-on". My
first thought would be to add something that would parallel the power-on
button and perform the function you describe.

But be careful how you implement this: you can design a one-shot using a
555 or 74123 (I'm showing my age), but remember that when the power is
coming up, some devices' behavior may be unpredictable.

If I were designing something like that, I would do at least two things:
a) don't apply power to your circuit until it's been up for (say) 2
seconds, and b) if the 741 doesn't come to life (check backlighting
voltage, etc.) then re-cycle the power switch.

Another possibility, although primitive, would be to use a solenoid that
would physically press the power button, which wouldn't require
electrical modifications to the radio.

My two cents.....

73, good luck, and let us know what you do!

Dave
KZ1O


tirebouchon69 wrote:

Hi,
I want to use my Kenwood TM-741 transceiver as an APRS transmitter in my
car. I plug my APRS system on Ignition 12v power, so it powers on
automatically when I start the engine.

The problem I have is with the TM-741: when 12v DC power is applied to it,
it doesn't power up automatically; i have to press on "power" button every
time. TM-741 CPU doesn't memorise power state when 12v power is cut.

Is there a modification or a programmation I could do to allow it to power
up automatically when 12v supply is applied to it? Any idea ?

Thank you in advance.

Daniel VE2BAP, Montreal, Canada

Hi Dave,
I was also thinking to this kind of solution. after "ohe-shot" by-passing
power-up button (a 555 timer as you say), I could detect if radio has
powered on by sensing light on display with a photo-cell.

I finally decided to bring back to life my old Icom IC-22S (10 watts VHF
transceiver) and use it for APRS; It is already modified for packet
frequencies. But I could still modify my TM-741 (for auto power-up) if I
need more power...

Thanks for advices.
Daniel VE2BAP

"Dave Bushong" wrote in message
. net...
Hi Corkscrew,

Unfortunately, the 741 doesn't have a setting for "auto-power-on". My
first thought would be to add something that would parallel the power-on
button and perform the function you describe.

But be careful how you implement this: you can design a one-shot using a
555 or 74123 (I'm showing my age), but remember that when the power is
coming up, some devices' behavior may be unpredictable.

If I were designing something like that, I would do at least two things:
a) don't apply power to your circuit until it's been up for (say) 2
seconds, and b) if the 741 doesn't come to life (check backlighting
voltage, etc.) then re-cycle the power switch.

Another possibility, although primitive, would be to use a solenoid that
would physically press the power button, which wouldn't require
electrical modifications to the radio.

My two cents.....

73, good luck, and let us know what you do!

Dave
KZ1O


tirebouchon69 wrote:

Hi,
I want to use my Kenwood TM-741 transceiver as an APRS transmitter in my
car. I plug my APRS system on Ignition 12v power, so it powers on
automatically when I start the engine.

The problem I have is with the TM-741: when 12v DC power is applied to
it,
it doesn't power up automatically; i have to press on "power" button
every
time. TM-741 CPU doesn't memorise power state when 12v power is cut.

Is there a modification or a programmation I could do to allow it to
power
up automatically when 12v supply is applied to it? Any idea ?

Thank you in advance.

Daniel VE2BAP, Montreal, Canada