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Internet interface
Posted: Fri Jul 16, 2021 6:56 am
by TomXP411
14 hours ago, BruceMcF said:
If it's industrial equipment, it might be 5v tolerant, since voltage drops with longer cable runs ... it would be fortunate if that was true, so you only have to convert voltage on the input lines.
I'm not sure what you mean there... the Altairduino runs on an Arduino and requires a MAX232 chip in order to convert TTL to RS-232. Likewise, the Commander X16 will require level converters when connecting to basically any 32-bit microcontroller, since most are not 5v tolerant. The Raspberry Pi definitely is not.
Internet interface
Posted: Fri Jul 16, 2021 8:17 am
by BruceMcF
1 hour ago, TomXP411 said:
I'm not sure what you mean there... the Altairduino runs on an Arduino and requires a MAX232 chip in order to convert TTL to RS-232. Likewise, the Commander X16 will require level converters when connecting to basically any 32-bit microcontroller, since most are not 5v tolerant. The Raspberry Pi definitely is not.
I wasn't talking about the Altairduino, I was talking about the RS-232C to Ethernet box. The spec range of RS-232C is +3V<Logic0<+15V and -15V<Logic1<-3V, so if it's a direct connection, it would tolerate a very simple level conversion circuit.
Internet interface
Posted: Sat Jul 17, 2021 5:28 pm
by TomXP411
On 7/16/2021 at 1:17 AM, BruceMcF said:
I wasn't talking about the Altairduino, I was talking about the RS-232C to Ethernet box. The spec range of RS-232C is +3V<Logic0<+15V and -15V<Logic1<-3V, so if it's a direct connection, it would tolerate a very simple level conversion circuit.
A max232 based shifter with pre-soldered DE9 is like $3 on Amazon...
Internet interface
Posted: Sat Jul 17, 2021 5:55 pm
by rje
27 minutes ago, TomXP411 said:
A max232 based shifter with pre-soldered DE9 is like $3 on Amazon...
Now that's my price point!
https://en.wikipedia.org/wiki/MAX232:
Quote
The MAX232 is an integrated circuit first created in 1987 by Maxim Integrated Products that converts signals from a TIA-232 (RS-232) serial port to signals suitable for use in TTL-compatible digital logic circuits. The MAX232 is a dual transmitter / dual receiver that typically is used to convert the RX, TX, CTS, RTS signals.
The drivers provide TIA-232 voltage level outputs (about ±7.5 volts) from a single 5-volt supply by on-chip charge pumps and external capacitors. This makes it useful for implementing TIA-232 in devices that otherwise do not need any other voltages.
The receivers reduce TIA-232 inputs, which may be as high as ±25 volts, to standard 5 volt TTL levels. These receivers have a typical threshold of 1.3 volts and a typical hysteresis of 0.5 volts.
Internet interface
Posted: Sat Jul 17, 2021 6:44 pm
by TomXP411
48 minutes ago, rje said:
Yeah, those are like $15 for 5 units, and it's a complete, self-contained unit. So rolling a custom solution doesn't make a lot of sense, when modular solutions are cheap and easy to install.
Internet interface
Posted: Sat Jul 17, 2021 6:45 pm
by BruceMcF
59 minutes ago, TomXP411 said:
A max232 based shifter with pre-soldered DE9 is like $3 on Amazon...
Aren't economies of scale great? That's lower than the Q25 Mouser price of a 10ns PDIP MAX232's.
With +/-12V available, as simple transistor based circuit would still be cheaper, but that's cheap enough it's not going to be noticeable.