Analog Output - Revision history

DanJohnson at 15:18, 9 December 2008

2008-12-09T15:18:59Z

← Older revision		Revision as of 10:18, 9 December 2008
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	The i2c bus lines are wired in common to all i2c slave devices; here we have just two MAX517 DAC chips. Each slave must have a different one-byte address. In the case of the MAX517, six of the bits of this address are fixed by the manufacturer and two are selected by you when wiring the chip. In binary the address is 0101 1**0, or in hex 0x58, ~~0x59~~, ~~0x5A~~, or ~~0x5B~~. The ~~last~~ two bits are chosen by wiring the AD1 and AD0 pins high or low. So in the circuit shown we can address the two DACs as 0x58 and ~~0x59~~. (The prefix 0x means "this is a hexidecimal number")		The i2c bus lines are wired in common to all i2c slave devices; here we have just two MAX517 DAC chips. Each slave must have a different one-byte address. In the case of the MAX517, six of the bits of this address are fixed by the manufacturer and two are selected by you when wiring the chip. In binary the address is 0101 1**0, or in hex 0x58, 0x5A, 0x5C, or 0x5E. The two variable bits are chosen by wiring the AD1 and AD0 pins high or low. So in the circuit shown we can address the two DACs as 0x58 and 0x5A. (The prefix 0x means "this is a hexidecimal number")

DanJohnson at 15:07, 9 December 2008

2008-12-09T15:07:04Z

← Older revision		Revision as of 10:07, 9 December 2008
Line 23:		Line 23:


	The i2c bus lines are wired in common to all i2c slave devices; here we have just two MAX517 DAC chips. Each slave must have a different one-byte address. In the case of the MAX517, six of the bits of this address are fixed by the manufacturer and two are selected by you when wiring the chip. In binary the address is 0101 10**, or in hex 0x58, 0x59, 0x5A, or 0x5B. The last two bits are chosen by wiring the AD1 and AD0 pins high or low. So in the circuit shown we can address the two DACs as 0x58 and 0x59. (The prefix 0x means "this is a hexidecimal number")		The i2c bus lines are wired in common to all i2c slave devices; here we have just two MAX517 DAC chips. Each slave must have a different one-byte address. In the case of the MAX517, six of the bits of this address are fixed by the manufacturer and two are selected by you when wiring the chip. In binary the address is 0101 1**0, or in hex 0x58, 0x59, 0x5A, or 0x5B. The last two bits are chosen by wiring the AD1 and AD0 pins high or low. So in the circuit shown we can address the two DACs as 0x58 and 0x59. (The prefix 0x means "this is a hexidecimal number")


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	i2c_start(); // take control of the bus; impose "start" levels		i2c_start(); // take control of the bus; impose "start" levels
	i2c_write(0x58); // address. 0101 ~~1000~~. ~~Last~~ 2 bits are selected by 2 pins high or low on MAX517		i2c_write(0x58); // address. 0101 1<font color="#FF0000">00</font>0. Red bits are selected by 2 pins high or low on MAX517
	i2c_write(0); // command. just zero		i2c_write(0); // command. just zero
	i2c_write(i); // data. Translated to analog output voltage		i2c_write(i); // data. Translated to analog output voltage

LIMS at 02:52, 3 January 2008

2008-01-03T02:52:42Z

← Older revision		Revision as of 21:52, 2 January 2008
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	* Connect 8 digital output lines (perhaps the whole D port) to a parallel DAC chip (digital to analog converter) such as the DAC0800. That's a lot of wires, and uses up a lot of your PIC pins, but it's conceptually simple. An instruction such as output_D(ivalue) is then all you need: ivalue=0 becomes 0V and ivalue=255 becomes 5V.		* Connect 8 digital output lines (perhaps the whole D port) to a parallel DAC chip (digital to analog converter) such as the DAC0800. That's a lot of wires, and uses up a lot of your PIC pins, but it's conceptually simple. An instruction such as output_D(ivalue) is then all you need: ivalue=0 becomes 0V and ivalue=255 becomes 5V.

	* Use a serial DAC chip such as the MAX517, as described next. This requires only 2 communication wires, and ~~many~~ DAC chips (and other chips) can ~~be addressed on~~ the same bus.		* Use a serial DAC chip such as the MAX517, as described next. This requires only 2 communication wires, and several DAC chips (and other chips) can share the same bus.


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	To command the DAC, see the code MAX517.c in AnalogOutput. The ~~keys~~ ~~lines~~ ~~are the one that sets up~~ the i2c controller, ~~and~~ ~~then~~ ~~lines~~ to take control of the bus, send the address byte (0x58), the command byte (0), and the desired data byte (i in this case)		To command the DAC, see the code MAX517.c in AnalogOutput. The "#USE" line configures the i2c controller. Subsequent i2c instructions to take control of the bus, send the address byte (0x58), the command byte (0), and the desired data byte (i in this case), and release the bus.

LIMS at 05:09, 30 December 2007

2007-12-30T05:09:07Z

← Older revision		Revision as of 00:09, 30 December 2007
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	* Use a PWM output. The duty cycle range of 0% to 100% implies an average output voltage between 0V and 5V. You can use an RC low-pass filter to smooth the output. The smoother you make it, the slower it will be to reflect changes in the duty cycle.		* Use a PWM output. The duty cycle range of 0% to 100% implies an average output voltage between 0V and 5V. You can use an RC low-pass filter to smooth the output. The smoother you make it, the slower it will be to reflect changes in the duty cycle.

	* Connect 8 digital output lines to a parallel DAC chip (digital to analog converter) such as the ~~ADC0820~~. That's a lot of wires, and a ~~20-pin~~ ~~chip~~, but it's conceptually simple. An instruction such as output_D(ivalue) is then all you need: ivalue=0 becomes 0V and ivalue=255 becomes 5V.		* Connect 8 digital output lines (perhaps the whole D port) to a parallel DAC chip (digital to analog converter) such as the DAC0800. That's a lot of wires, and uses up a lot of your PIC pins, but it's conceptually simple. An instruction such as output_D(ivalue) is then all you need: ivalue=0 becomes 0V and ivalue=255 becomes 5V.

	* Use a serial DAC chip such as the MAX517, as described next. This requires only 2 communication wires, and many DAC chips (and other chips) can be addressed on the same bus.		* Use a serial DAC chip such as the MAX517, as described next. This requires only 2 communication wires, and many DAC chips (and other chips) can be addressed on the same bus.

LIMS at 05:03, 30 December 2007

2007-12-30T05:03:16Z

← Older revision		Revision as of 00:03, 30 December 2007
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	The PIC has 13 analog inputs, but no analog outputs. If you need an analog output there are at least three ways to get it:		The PIC has 13 analog inputs, but no analog outputs. If you need an analog output there are at least three ways to get it:


	* Use a PWM output. The duty cycle range of 0% to 100% implies an average output voltage between 0V and 5V. You can use an RC low-pass filter to smooth the output. The smoother you make it, the slower it will be to reflect changes in the duty cycle.		* Use a PWM output. The duty cycle range of 0% to 100% implies an average output voltage between 0V and 5V. You can use an RC low-pass filter to smooth the output. The smoother you make it, the slower it will be to reflect changes in the duty cycle.

LIMS at 05:02, 30 December 2007

2007-12-30T05:02:33Z

← Older revision		Revision as of 00:02, 30 December 2007
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	[[Image:i2c-dac.gif\|right]]		[[Image:i2c-dac.gif\|right]]

	<b>Wiring an ~~12c~~ bus</b>		<b>Wiring an i2c bus</b>

	We'll illustrate an i2c bus with two MAX517 DAC chips. The SCL and SDA lines need pull-up resistors as shown. (Without them, i2c instructions cause the PIC to wait forever for the bus to clear.)		We'll illustrate an i2c bus with two MAX517 DAC chips. The SCL and SDA lines need pull-up resistors as shown. (Without them, i2c instructions cause the PIC to wait forever for the bus to clear.)

LIMS at 05:02, 30 December 2007

2007-12-30T05:02:17Z

← Older revision		Revision as of 00:02, 30 December 2007
Line 1:		Line 1:
	The PIC ~~doesn't~~ ~~have any~~ analog ~~outputs~~, ~~even~~ ~~though it has 13~~ analog ~~inputs~~. If you need analog output there are at least three ways to get it:		The PIC has 13 analog inputs, but no analog outputs. If you need an analog output there are at least three ways to get it:

⚫	* Use a PWM output. The duty cycle range 0% to 100% implies an average output voltage between 0V and 5V. You can use an RC low-pass filter to smooth the output. The smoother you ~~want~~ it, the slower it is to reflect changes in the duty cycle.

		⚫	* Use a PWM output. The duty cycle range of 0% to 100% implies an average output voltage between 0V and 5V. You can use an RC low-pass filter to smooth the output. The smoother you make it, the slower it will be to reflect changes in the duty cycle.
⚫	* Connect 8 digital output lines to a ~~simple~~ DAC chip (digital to analog converter) such as the ADC0820. That's a lot of wires, and a 20-pin chip, but it's conceptually simple.

		⚫	* Connect 8 digital output lines to a parallel DAC chip (digital to analog converter) such as the ADC0820. That's a lot of wires, and a 20-pin chip, but it's conceptually simple. An instruction such as output_D(ivalue) is then all you need: ivalue=0 becomes 0V and ivalue=255 becomes 5V.
⚫	* Use a serial DAC chip such as the MAX517, as described next. This requires only 2 communication wires, and many DAC chips (and other chips) can be addressed.

		⚫	* Use a serial DAC chip such as the MAX517, as described next. This requires only 2 communication wires, and many DAC chips (and other chips) can be addressed on the same bus.


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	There are a lot of chips available that communicate via a serial protocol called i2c ("i squared c"). This requires only two communication lines: SCL and SDA (plus a common ground of course). SCL refers to a CLock signal and SDA to a stream of DAta bits. Many chips can share this 2-wire bus. The PIC would ordinarily be Bus Master, and select whichever chip it wishes to talk to by sending a one-byte address code. PIC-to-PIC communication can also be set up using i2c.		There are a lot of chips available that communicate via a serial protocol called i2c ("i squared c"). This requires only two communication lines: SCL and SDA (plus a common ground of course). SCL refers to a CLock signal and SDA to a stream of DAta bits. Many chips can share this 2-wire bus. The PIC would ordinarily be Bus Master, and select whichever chip it wishes to talk to by sending a one-byte address code. PIC-to-PIC communication can also be set up using i2c.


	The 4520 PIC can control the i2c bus lines using a hardware i2c controller, or a software controller. The timing of software-controlled bus signals can be disrupted by interrupts, so hardware is often preferable. The software controller can use any pins for SCL and SDA. The hardware controller can only use RC3 and RC4. Sadly RC3 is just about the only pin that is NOT available at the 4520 board's edge connector, but you can connect to it on the PCB itself near pin 18 of the PIC 4520.		The 4520 PIC can control the i2c bus lines using a hardware i2c controller, or a software controller. The timing of software-controlled bus signals can be disrupted by interrupts, so hardware is often preferable. The software controller can use any pins for SCL and SDA. The hardware controller can only use RC3 and RC4. Sadly RC3 is just about the only pin that is NOT available at the 4520 board's edge connector, but you can connect to it on the PCB itself near pin 18 of the PIC 4520.
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	We'll illustrate an i2c bus with two MAX517 DAC chips. The SCL and SDA lines need pull-up resistors as shown. (Without them, i2c instructions cause the PIC to wait forever for the bus to clear.)		We'll illustrate an i2c bus with two MAX517 DAC chips. The SCL and SDA lines need pull-up resistors as shown. (Without them, i2c instructions cause the PIC to wait forever for the bus to clear.)


	The i2c bus lines are wired in common to all i2c slave devices; here we have just two MAX517 DAC chips. Each slave must have a different one-byte address. In the case of the MAX517, six of the bits of this address are fixed by the manufacturer and two are selected by you when wiring the chip. In binary the address is 0101 10**, or in hex 0x58, 0x59, 0x5A, or 0x5B. The last two bits are chosen by wiring the AD1 and AD0 pins high or low. So in the circuit shown we can address the two DACs as 0x58 and 0x59. (The prefix 0x means "this is a hexidecimal number")		The i2c bus lines are wired in common to all i2c slave devices; here we have just two MAX517 DAC chips. Each slave must have a different one-byte address. In the case of the MAX517, six of the bits of this address are fixed by the manufacturer and two are selected by you when wiring the chip. In binary the address is 0101 10**, or in hex 0x58, 0x59, 0x5A, or 0x5B. The last two bits are chosen by wiring the AD1 and AD0 pins high or low. So in the circuit shown we can address the two DACs as 0x58 and 0x59. (The prefix 0x means "this is a hexidecimal number")


	The PIC is then responsible to send a series of bytes to control a DAC. It sends an address byte to make the proper chip pay attention, then a command byte which for these simple chips is just zero, and then a data byte containing the value to convert to analog: value 0 becomes 0V and value 255 becomes 5V.		The PIC is then responsible to send a series of bytes to control a DAC. It sends an address byte to make the proper chip pay attention, then a command byte which for these simple chips is just zero, and then a data byte containing the value to convert to analog: value 0 becomes 0V and value 255 becomes 5V.
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	The DAC has a Vref input, which scales the output voltage. If you tie Vref to +5V, the output voltage ranges 0V to 5V, but also any noise on the 5V rail will become noise on the DAC's output. You can use a cleaner Vref if you wish. See the MAX517 documentation.		The DAC has a Vref input, which scales the output voltage. If you tie Vref to +5V, the output voltage ranges 0V to 5V, but also any noise on the 5V rail will become noise on the DAC's output. You can use a cleaner Vref if you wish. See the MAX517 documentation.


	To command the DAC, see the code MAX517.c in AnalogOutput. The keys lines are the one that sets up the i2c controller, and then lines to take control of the bus, send the address byte (0x58), the command byte (0), and the desired data byte (i in this case)		To command the DAC, see the code MAX517.c in AnalogOutput. The keys lines are the one that sets up the i2c controller, and then lines to take control of the bus, send the address byte (0x58), the command byte (0), and the desired data byte (i in this case)


	#use i2c(MASTER, FAST, SCL=PIN_C3, SDA=PIN_C4, FORCE_HW) // use hardware i2c controller		#use i2c(MASTER, FAST, SCL=PIN_C3, SDA=PIN_C4, FORCE_HW) // use hardware i2c controller

LIMS at 01:08, 30 December 2007

2007-12-30T01:08:10Z

← Older revision		Revision as of 20:08, 29 December 2007
Line 32:		Line 32:
	To command the DAC, see the code MAX517.c in AnalogOutput. The keys lines are the one that sets up the i2c controller, and then lines to take control of the bus, send the address byte (0x58), the command byte (0), and the desired data byte (i in this case)		To command the DAC, see the code MAX517.c in AnalogOutput. The keys lines are the one that sets up the i2c controller, and then lines to take control of the bus, send the address byte (0x58), the command byte (0), and the desired data byte (i in this case)

	#use i2c(~~Master~~, ~~Fast~~, ~~sda~~=~~PIN_C4~~,~~scl~~=~~PIN_C3~~, ~~force_hw~~) // use hardware i2c controller		#use i2c(MASTER, FAST, SCL=PIN_C3, SDA=PIN_C4, FORCE_HW) // use hardware i2c controller

	i2c_start(); // take control of the bus; impose "start" levels		i2c_start(); // take control of the bus; impose "start" levels

LIMS at 01:06, 30 December 2007

2007-12-30T01:06:20Z

← Older revision		Revision as of 20:06, 29 December 2007
Line 21:		Line 21:
	We'll illustrate an i2c bus with two MAX517 DAC chips. The SCL and SDA lines need pull-up resistors as shown. (Without them, i2c instructions cause the PIC to wait forever for the bus to clear.)		We'll illustrate an i2c bus with two MAX517 DAC chips. The SCL and SDA lines need pull-up resistors as shown. (Without them, i2c instructions cause the PIC to wait forever for the bus to clear.)

	The i2c bus lines are wired in common to all i2c slave devices; here we have just two MAX517 DAC chips. Each slave must have a different one-byte address. In the case of the MAX517, six of the bits of this address are fixed by the manufacturer and two are selected by you when wiring the chip. In binary the address is 0101 10**, or in hex 0x58, 0x59, 0x5A, or 0x5B. The last two bits are chosen by wiring the AD1 and AD0 pins high or low. So in the circuit shown we can address the two DACs as 0x58 and 0x59.		The i2c bus lines are wired in common to all i2c slave devices; here we have just two MAX517 DAC chips. Each slave must have a different one-byte address. In the case of the MAX517, six of the bits of this address are fixed by the manufacturer and two are selected by you when wiring the chip. In binary the address is 0101 10**, or in hex 0x58, 0x59, 0x5A, or 0x5B. The last two bits are chosen by wiring the AD1 and AD0 pins high or low. So in the circuit shown we can address the two DACs as 0x58 and 0x59. (The prefix 0x means "this is a hexidecimal number")

	The PIC is then responsible to send a series of bytes to control a DAC. It sends an address byte to make the proper chip pay attention, then a command byte which for these simple chips is just zero, and then a data byte containing the value to convert to analog: value 0 becomes 0V and value 255 becomes 5V.		The PIC is then responsible to send a series of bytes to control a DAC. It sends an address byte to make the proper chip pay attention, then a command byte which for these simple chips is just zero, and then a data byte containing the value to convert to analog: value 0 becomes 0V and value 255 becomes 5V.

LIMS at 01:05, 30 December 2007

2007-12-30T01:05:21Z

← Older revision		Revision as of 20:05, 29 December 2007
Line 21:		Line 21:
	We'll illustrate an i2c bus with two MAX517 DAC chips. The SCL and SDA lines need pull-up resistors as shown. (Without them, i2c instructions cause the PIC to wait forever for the bus to clear.)		We'll illustrate an i2c bus with two MAX517 DAC chips. The SCL and SDA lines need pull-up resistors as shown. (Without them, i2c instructions cause the PIC to wait forever for the bus to clear.)

	The i2c bus lines are wired in common to all i2c slave devices; here we have just two MAX517 DAC chips. Each slave must have a different one-byte address. In the case of the MAX517, six of the bits of this address are fixed by the manufacturer and two are selected by you when wiring the chip. In binary the address is 0101 10--, or in hex 0x58, 0x59, 0x5A, or 0x5B. The last two bits are chosen by wiring the AD1 and AD0 pins high or low. So in the circuit shown we can address the two DACs as 0x58 and 0x59.		The i2c bus lines are wired in common to all i2c slave devices; here we have just two MAX517 DAC chips. Each slave must have a different one-byte address. In the case of the MAX517, six of the bits of this address are fixed by the manufacturer and two are selected by you when wiring the chip. In binary the address is 0101 10**, or in hex 0x58, 0x59, 0x5A, or 0x5B. The last two bits are chosen by wiring the AD1 and AD0 pins high or low. So in the circuit shown we can address the two DACs as 0x58 and 0x59.

	The PIC is then responsible to send a series of bytes to control a DAC. It sends an address byte to make the proper chip pay attention, then a command byte which for these simple chips is just zero, and then a data byte containing the value to convert to analog: value 0 becomes 0V and value 255 becomes 5V.		The PIC is then responsible to send a series of bytes to control a DAC. It sends an address byte to make the proper chip pay attention, then a command byte which for these simple chips is just zero, and then a data byte containing the value to convert to analog: value 0 becomes 0V and value 255 becomes 5V.