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

[Harry McNally]

Hi Adrian

Yes, BC549 should do the trick. I realised I actually built something like 
this a while ago for someone else which ISTR was for weatherfax (yachtie project).

All the best
Harry

On 16/11/13 20:54, Adrian Woodley wrote:
> Cheers Harry, that's given me something to work with.
>
> I should be able to substitute the PN2222A with BC549 right? I have a bunch of
> them on hand, which saves me a trip to Jaycar.
>
> Adrian
>
> On 14/11/13 23:46, Harry McNally wrote:
>> 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
>>> ------------------------------------------------------------------------------
>>>
>>> PLUG discussion list: plug at plug.org.au
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>>>
>>>
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>> _______________________________________________
>> PLUG discussion list: plug at plug.org.au
>> http://lists.plug.org.au/mailman/listinfo/plug
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>
> _______________________________________________
> PLUG discussion list: plug at plug.org.au
> http://lists.plug.org.au/mailman/listinfo/plug
> Committee e-mail: committee at plug.org.au
> PLUG Membership: http://www.plug.org.au/membership
>