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

[Adrian Woodley]

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
>> ------------------------------------------------------------------------------
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