[plug] [Off-topic] CMOS 3V3 to TTL 5v buffer

[Harry McNally]

Hi Adrian, Euan

Just wondering if an opto-isolator might be better mainly to avoid a ground 
loop between the two units (or allow separate supplies for the RPi and 
transceiver). But you'd need 5V on the transceiver connector (or a regulator 
on the transceiver side supply) for a pullup resistor if there isn't one 
(inside) as part of the transceiver interface.

Here is a simple MIDI one with the general idea:

http://irq5.files.wordpress.com/2011/03/midi-sch.png

Ah. Having looked at the C-IV it appears to be bi-directional. Ignoring the 
opto-isolation idea, here is a circuit that may run from 3.3 volts on the RPi 
side:

http://www.qsl.net/g3vgr/civ.html

Ignore the RS-232 and feed 3.3 volts across the 10uF cap. Delete the IN914 
(both) and feed the TTL serial TX pin from the RPi to the 10K resistor (the 
DP9 pin 3. Feed the signal at DP9 pin 2 to the RPi TTL RX input.

It's a shame that the ICOM doesn't pull the tip signal to 5V internally 
(perhaps it does). If it does, you can delete the 4K7 resistor on the top left 
and the ICOM will pull the signal to the appropriate level.

PTT is also available on that circuit too. Delete the IN914 and 4K7 pull-down 
resistor. You won't need them for TTL (3.3V) digital out from the RPi.

Hope that all makes sense.

All the best
Harry

On 14/11/13 21:49, Euan de Kock wrote:
> If your only running it in one direction, eg as an output, then the easiest is
> through a 74LS01 twice - the 7401 is a logic inverter, and can work at a much
> higher frequency than 19200. The logic levels on most 74 devices are such that
> 3.3v is more than enough to register as true logic.
>
> Regards,
>
> Euan deKock.
>
> Adrian Woodley <Adrian at Diskworld.com.au> wrote:
>
>     G'day PLUGers,
>
>     A little off topic, but I'm looking for a simple CMOS to TTL buffer /
>     level converter. The plan is to use a RPi (3V3 CMOS) to control an Icom
>     IC-7400 transceiver, using the Cat C-IV interface (5V TTL). Needs to
>     handle 19200 baud.
>
>     Cheers,
>
>     Adrian
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