Converting to TTL levels
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Posts: 46,084
Hi All,
I am working on a project that requires me to decode 9 bits (9 input
pins) of binary code that may (unusually) be high at +28V, (30V
absolute max). The same input pins need to have the flexability to
work with +12V highs. All lows are ground level.
Can anyone suggest a way that I can convert these input parameters
so that the stamp can deal with them? Is there an IC package that
converts higher voltages to TTL levels?
REgards,
Dwain.
I am working on a project that requires me to decode 9 bits (9 input
pins) of binary code that may (unusually) be high at +28V, (30V
absolute max). The same input pins need to have the flexability to
work with +12V highs. All lows are ground level.
Can anyone suggest a way that I can convert these input parameters
so that the stamp can deal with them? Is there an IC package that
converts higher voltages to TTL levels?
REgards,
Dwain.
Comments
dwainsworld@e... writes:
> Hi All,
>
> I am working on a project that requires me to decode 9 bits (9 input
> pins) of binary code that may (unusually) be high at +28V, (30V
> absolute max). The same input pins need to have the flexability to
> work with +12V highs. All lows are ground level.
>
> Can anyone suggest a way that I can convert these input parameters
> so that the stamp can deal with them? Is there an IC package that
> converts higher voltages to TTL levels?
>
> REgards,
>
> Dwain.
Dwain,
You can easily convert the 12 to 28 volts to TTL level signals. Two options
immeadiately come to mind.
1) use a 2n3904 transistor......connect emitter to ground, connect the
collector to one end of a 4.7k ohm resistor, the other end of the 4.7k ohm
resistor to +5v.
Also connect the colloector to the stamp input pin (many suggest to do this
through a resistor for protection - 100 ohms should be sufficient)
Connect 300k (or 500k) ohms to the base of the transistor. Connect your 12 to
28 volt source to the other end of the 300k ohm resistor.
When 12 to 24 volts is present, the stamp will recieve a logic zero and visa
versa. If the transistor must switch on and off really fast......The resistor
values and circuit will need some tuning to speed up the turn on and turn off
time of the interface circuit. The values used are just a starting point if
switching speed is not a concern.
2) the second idea is to use an opto isolator (4n35).
If you need more clarification on either idea, write back, or send me a FAX
number off list and I can send you a schematic.....
Ken
[noparse][[/noparse]Non-text portions of this message have been removed]
From the signal line, connect one end of a 5 k Ohm resistor. To the
other end of the resistor connect the cathode end of a 5.1 Volt zener
diode. Ground the anode end of the zener. The junction of the zener
and the resistor will go from +5.1 Volts to -0.5 Volts, which is within
the design guidelines for ttl logic.
Original Message
From: smartdim@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=IftvewWMcJWABxChBI_NVFZmSwyveFL5han13kVIuFzmh8g_oYoEhLNrfzEyqh4UXLtObqnJobKy7sk]smartdim@a...[/url
Sent: Tuesday, April 15, 2003 10:12 AM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] Converting to TTL levels
In a message dated 4/15/2003 5:51:46 AM Pacific Daylight Time,
dwainsworld@e... writes:
> Hi All,
>
> I am working on a project that requires me to decode 9 bits (9 input
> pins) of binary code that may (unusually) be high at +28V, (30V
> absolute max). The same input pins need to have the flexability to
> work with +12V highs. All lows are ground level.
>
> Can anyone suggest a way that I can convert these input parameters
> so that the stamp can deal with them? Is there an IC package that
> converts higher voltages to TTL levels?
>
> REgards,
>
> Dwain.
Dwain,
You can easily convert the 12 to 28 volts to TTL level signals. Two
options
immeadiately come to mind.
1) use a 2n3904 transistor......connect emitter to ground, connect the
collector to one end of a 4.7k ohm resistor, the other end of the 4.7k
ohm
resistor to +5v.
Also connect the colloector to the stamp input pin (many suggest to do
this
through a resistor for protection - 100 ohms should be sufficient)
Connect 300k (or 500k) ohms to the base of the transistor. Connect your
12 to
28 volt source to the other end of the 300k ohm resistor.
When 12 to 24 volts is present, the stamp will recieve a logic zero and
visa
versa. If the transistor must switch on and off really fast......The
resistor
values and circuit will need some tuning to speed up the turn on and
turn off
time of the interface circuit. The values used are just a starting point
if
switching speed is not a concern.
2) the second idea is to use an opto isolator (4n35).
If you need more clarification on either idea, write back, or send me a
FAX
number off list and I can send you a schematic.....
Ken
[noparse][[/noparse]Non-text portions of this message have been removed]
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