westaust55
Moderator
Occasionally the need arises to interface the PICAXE to another IC that needs to operate at a different voltage.
Until recently most would operate their nominal 5V PICAXE chips at 4.5V or 5V and occasionally 3V. Now there are 3V options as well.
Occasionally there are chips that must operate around 5V. The DS1307 RTC is such an IC having a minimum operating voltage of 4.5V.
EEPROMS such as the 24LC256 can operate at 3.3V or 5V quite happily.
Other new ICs and modules operate at voltages in the ranges such as 2V to 3.6V
Even the gLCD modules some of us have used out of mobile phones such as the Siemens A55 and Nokia 3310 operate at 3V.
In the past, there has occasionally been reference to use of two resistors as a potential divider. Examples include a 10K over a 20k (2 x 10k) resistor or a 4.7K over a 6.8k resistor are some examples.
Around a year ago I had purchased a few 74HC245 bi-directional 3-state octal bus transceivers but then had to put a resistor divider in from of the inputs.
It came to my attention shortly thereafter than there is a 74LVC range of IC's intended to operate at around 3V which have 5V tolerant inputs. I subsequently purchased a few 74LVC245A chips but they and seemingly most of the 74LVC range available come in SOIC surface mounting packages.
Tonight I finally got around to mounting one of these 74LVC245A chips on a 20 pin SOIC to DIP adapter board.
Contrary to "best" practice, I clamped the IC in place on the adapter board and successfully soldered it with a standard soldering iron.
Put it to the test with an ex A55 gLCD module and all worked perfectly.
Couple of photos showing the old 74HC245 board and the new 74LVC245A board for comparison. while having to buy the SOIC to DIP adapter has an added cost, it saves me 16 resistors per module so the cost roughly balances out and provides a far simpler schematic and circuit.
So in conclusion,
- where you have just 1 or 2 signals, a couple of resistors can be quick and effective
- where you want up to 8 signals with level switching even with switched/controlled bi-directional capability consider the 74LVC245A
- as I mentioned in a recent post, if you need bidirectional level switching with "automatic" direction change such as for an i2c bus consider using a couple of FET transistors such as the 2N7000. No other components required - just connect as per the philips app note AN97055 .
Trust others might find this information useful.
Until recently most would operate their nominal 5V PICAXE chips at 4.5V or 5V and occasionally 3V. Now there are 3V options as well.
Occasionally there are chips that must operate around 5V. The DS1307 RTC is such an IC having a minimum operating voltage of 4.5V.
EEPROMS such as the 24LC256 can operate at 3.3V or 5V quite happily.
Other new ICs and modules operate at voltages in the ranges such as 2V to 3.6V
Even the gLCD modules some of us have used out of mobile phones such as the Siemens A55 and Nokia 3310 operate at 3V.
In the past, there has occasionally been reference to use of two resistors as a potential divider. Examples include a 10K over a 20k (2 x 10k) resistor or a 4.7K over a 6.8k resistor are some examples.
Around a year ago I had purchased a few 74HC245 bi-directional 3-state octal bus transceivers but then had to put a resistor divider in from of the inputs.
It came to my attention shortly thereafter than there is a 74LVC range of IC's intended to operate at around 3V which have 5V tolerant inputs. I subsequently purchased a few 74LVC245A chips but they and seemingly most of the 74LVC range available come in SOIC surface mounting packages.
Tonight I finally got around to mounting one of these 74LVC245A chips on a 20 pin SOIC to DIP adapter board.
Contrary to "best" practice, I clamped the IC in place on the adapter board and successfully soldered it with a standard soldering iron.
Put it to the test with an ex A55 gLCD module and all worked perfectly.
Couple of photos showing the old 74HC245 board and the new 74LVC245A board for comparison. while having to buy the SOIC to DIP adapter has an added cost, it saves me 16 resistors per module so the cost roughly balances out and provides a far simpler schematic and circuit.
So in conclusion,
- where you have just 1 or 2 signals, a couple of resistors can be quick and effective
- where you want up to 8 signals with level switching even with switched/controlled bi-directional capability consider the 74LVC245A
- as I mentioned in a recent post, if you need bidirectional level switching with "automatic" direction change such as for an i2c bus consider using a couple of FET transistors such as the 2N7000. No other components required - just connect as per the philips app note AN97055 .
Trust others might find this information useful.
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