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TTL or CMOS — Parallax Forums

TTL or CMOS

fltcmdrfltcmdr Posts: 14
edited 2010-08-09 04:42 in BASIC Stamp
I have a choice of using TTL or CMOS circuits for a stepper interogator. An abundant supply of 12volts. CMOS uses 12 volts so that would be an obvious choice. but I have 128 ah power available so a dedicated 5 volt,6 volt 7.5 volt or other regulated source is also an option. Any thoughts

Comments

  • LeonLeon Posts: 7,620
    edited 2010-08-08 11:00
    TTL is obsolete and hasn't been used for new designs for many years. It has serious problems, which were overcome by the use of CMOS.
  • fltcmdrfltcmdr Posts: 14
    edited 2010-08-08 11:09
    Thanx.. that solidifies my decision
    MC
  • Tracy AllenTracy Allen Posts: 6,664
    edited 2010-08-08 12:10
    Be careful. Not all CMOS uses 12Volts. You are referring to the older 4000 series, which are still great and can be used on a wide range of power supplies, including the 5 Volt Vdd Stamp power supply. There are many newer CMOS series that can only be used at 5.5 Volts or lower.

    Depending on the motor/controller, your project may need a translator for voltage and current levels, say, from 12 to 5 Volts, or from 5 Volts 1mA to 12V at 1A.

    Another point of confusion is that you will hear, "TTL levels", in relation to the Stamp inputs. That refers to an input switching threshold of around 1.4 Volts, a level that is a carryover from the TTL logic family. But internally, the Stamp is CMOS, not TTL circuitry. The Stamp inputs interpret less than about 1.4 Volts as LOW, and greater than that as HIGH. On the other hand, "CMOS levels", are typically 1/2 of the power supply voltage, so, 2.5 Volts on a 5 Volts supply or 6 Volts on a 12 Volt supply for 4000 series CMOS.
  • anhingusanhingus Posts: 10
    edited 2010-08-08 17:14
    a problem with cmos is electrostatic sensitivity and slew rate. ttl - the 74ls series - is the better choice for driving buss-loads, usual fanout of 10.

    ttl is generally 5 volts where cmos can run between 3-20 volts or so. you might want to go to jameco, for instance, and check the manufacturer spec sheet for whatever chips you are thinking of using and consider voltage, current, and frequency limitations.

    switching response - ttl generally runs to 20-30 mHz whereas cmos can have problems at 1 mHz at the 5 volt level. cmos improves a great deal in this department at higher voltage levels.

    the only problem i see with ttl is the power requirement - not for battery operated stuff, as a general rule. with a strong power supply, a board full of ttl chips makes an excellent coffee cup warmer.
  • fltcmdrfltcmdr Posts: 14
    edited 2010-08-09 03:50
    Ok..
    well I have ordered the parallax stepper motor. And Im building the interogator with 4070 and 4027 ICs. Im using tip32 power transistors for the stepper drivers. I dont think I will have to have an output to the stamp from this circuit but it will recieve its step pulses from the stamp. Also on board this "robot" are two automotive type alternators. I can use automotive stereo noise filters to keep the noise away. So hopefully that wont be an issue.
    MC
  • LeonLeon Posts: 7,620
    edited 2010-08-09 04:42
    anhingus wrote: »
    a problem with cmos is electrostatic sensitivity and slew rate. ttl - the 74ls series - is the better choice for driving buss-loads, usual fanout of 10.

    ttl is generally 5 volts where cmos can run between 3-20 volts or so. you might want to go to jameco, for instance, and check the manufacturer spec sheet for whatever chips you are thinking of using and consider voltage, current, and frequency limitations.

    switching response - ttl generally runs to 20-30 mHz whereas cmos can have problems at 1 mHz at the 5 volt level. cmos improves a great deal in this department at higher voltage levels.

    the only problem i see with ttl is the power requirement - not for battery operated stuff, as a general rule. with a strong power supply, a board full of ttl chips makes an excellent coffee cup warmer.

    CMOS can be much faster than TTL, 100 MHz or more!
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