I agree that the Digital I/O Board is a great product that provides 8 high current outputs and 8 optically isolated digital inputs, all of which require 7 or fewer I/O pins. If higher currents and/or digital inputs were required I would be in 100% agreement, however for this application I feel it is overkill.
The ULN2803 can easily handlye driving 8 120mA loads simultaneously. As for protection, It has a darlington transistor pair as a driver along with a 2.7K resistor between the input pin and the base of the first transistor. That offers a reasonable degree of protection in case the output transistor shorts.
If minimizing Prop I/O pins to drive the output were a requirement I would suggest using a TPIC6595 which combines the functions of a '595 and a ULN2803 in one chip. One or more TPICS can be controlled by as few as 3 I/O pins and provide a large number of outputs.
@idbruce, Re: “The 74HC595 will run with just (3) I/O pins, however, with just (3) I/O pins hooked up I had some problems with floating data. I am a firm believer, although I have never proven it, that the 4TH I/O should also be hooked up to eliminate this behavior.”
You are absolutely correct. In fact for both the '595 and the TPIC when only using 3 I/O pins to drive the data, serial clock, and register clock pins the gate (/G) should be grounded or have a pulldown resistor to ground, and the serial register clear (/SCLR) should have a pullup resistor connected to Vcc.
No input signal should be left floating.
Yes, the Digital I/" board my be overkill persay. But in a previous post she mentioned proving to her boss that it could be done, which lead me to believe this project may be used in an industrial setting or simmilar. My expeariance in these kind of enviroments there is no such thing as over kill.
@marzec309 - I am not trying to kill any potential sale for Parallax, but if that is your theory, it sounds to me like your are throwing money at a possible future problem. (7) - TIP120 and (7) - 4N25 should surely prevent any future failure.
@marzec309 - I am not trying to kill any potential sale for Parallax, but if that is your theory, it sounds to me like your are throwing money at a possible future problem. (7) - TIP120 and (7) - 4N25 should surely prevent any future failure.
Ease up there idbruce. I wasn't telling her to go out and buy it, was just a suggestion, as I stated. As far as throwing money at a possible future problem. Yes, maybe but $80 is well spent money for a solid designed and finished product. Would you want to tell your boss that the expensive down time they just experienced was the cause of a and IC that cost less then a dollar. I don't think so. And yes the circuits described previously are very capable and similar to the Digital I/O Board, thus why I suggested it.
I briefly looked at the datasheet, but I forgot to check if they could be cascaded. I assume they can be like the 595s.
Bruce
Yes they can be cascaded just like the '595. I guess I should have said the 5 input signals and one serial out signal are the same as what is found on the '595. The circuit with the 7 TPICS I mentioned are cascaded, and I can update them all in less than 1milliSecond with the prop.
Inputs can be a voltage from 5-30VDC (AC compatible) and outputs can be either mechanical or solid state relays that can switch up to 12A loads, such as cooling fans, solenoids, heating elements and more.
I'm typing up an argument of the different options available to present as an argument for/against the different components that could be used to provide the 24v output and circuit protection needed. I'm considering playing around with a digital i/o board, since it is ready to go and the schematic has plenty of safety features built in to protect the circuit, but so far i haven't been able to find any documentation of the I/O board being used with the propeller, all the information/text/videos i've found refers to its use with PBASIC. Is there any literature about using the Digital I/O board with the propeller?
I'm typing up an argument of the different options available to present as an argument for/against the different components that could be used to provide the 24v output and circuit protection needed. I'm considering playing around with a digital i/o board, since it is ready to go and the schematic has plenty of safety features built in to protect the circuit, but so far i haven't been able to find any documentation of the I/O board being used with the propeller, all the information/text/videos i've found refers to its use with PBASIC. Is there any literature about using the Digital I/O board with the propeller?
I probably would not choose to use this board after reviewing the design. Better to roll my own. Lift the circuits I like maybe. Why? All relays are single pole, no double pole. Why not 3sp and 3dp or provisions for solid state relay? The Optos would have been better isolated so that they could be input as they are or output to say drive/communicate in a 20mA loop etc. And without a hard common connection.
As for using it, why not either dive right in if the I/O is compatible (and it appears to be ok as is or minimally adaptable), or lift the parts of the schematic you like and can use. Use leds and switches to simulate what you are monitoring / controlling until there is minimal chance of releasing the magic component smoke.
As for using it, why not either dive right in if the I/O is compatible (and it appears to be ok as is or minimally adaptable), or lift the parts of the schematic you like and can use. Use leds and switches to simulate what you are monitoring / controlling until there is minimal chance of releasing the magic component smoke.
Frank
yes, i was going to start with the digital i/o schematic and eventually just keep the components I would need. I think it would save time to start with that design and then step it down from there, vs. try and build it from scratch on my own.
I'm typing up an argument of the different options available to present as an argument for/against the different components that could be used to provide the 24v output and circuit protection needed. I'm considering playing around with a digital i/o board, since it is ready to go and the schematic has plenty of safety features built in to protect the circuit, but so far i haven't been able to find any documentation of the I/O board being used with the propeller, all the information/text/videos i've found refers to its use with PBASIC. Is there any literature about using the Digital I/O board with the propeller?
After looking over the schematic I am sure the board will work with the propeller. It uses a '595 to drive a ULN2803, a combination often used with the propeller, and one I have used often in my own circuits. If circuit protection is an issue then I would consider either driving solid state relays directly from the propeller pins, driving mechanical relays by TPICs with the TPICs control signals going through optoisolators, or some combination of those two options.
Comments
I briefly looked at the datasheet, but I forgot to check if they could be cascaded. I assume they can be like the 595s.
Bruce
Yes, the Digital I/" board my be overkill persay. But in a previous post she mentioned proving to her boss that it could be done, which lead me to believe this project may be used in an industrial setting or simmilar. My expeariance in these kind of enviroments there is no such thing as over kill.
(7) - 4N25 @ $0.26 each = $1.82
http://www.mouser.com/ProductDetail/Lite-On/4N25/?qs=sGAEpiMZZMu0f%252bT2bkVfug%2fGLWZgnOPs
(7) - TIP120 @ $0.70 = $4.90
http://www.mouser.com/ProductDetail/STMicroelectronics/TIP120/?qs=sGAEpiMZZMutXGli8Ay4kAuOt55Alb1HfBmmaSaISy0%3d
$6.72 + tax
EDIT: Not any failure, but you know what I mean
Bruce
Ease up there idbruce. I wasn't telling her to go out and buy it, was just a suggestion, as I stated. As far as throwing money at a possible future problem. Yes, maybe but $80 is well spent money for a solid designed and finished product. Would you want to tell your boss that the expensive down time they just experienced was the cause of a and IC that cost less then a dollar. I don't think so. And yes the circuits described previously are very capable and similar to the Digital I/O Board, thus why I suggested it.
END OF RANT.
Yes they can be cascaded just like the '595. I guess I should have said the 5 input signals and one serial out signal are the same as what is found on the '595. The circuit with the 7 TPICS I mentioned are cascaded, and I can update them all in less than 1milliSecond with the prop.
First paragraph from the product page
my mistake, i was reading 12V instead of 12A.
I probably would not choose to use this board after reviewing the design. Better to roll my own. Lift the circuits I like maybe. Why? All relays are single pole, no double pole. Why not 3sp and 3dp or provisions for solid state relay? The Optos would have been better isolated so that they could be input as they are or output to say drive/communicate in a 20mA loop etc. And without a hard common connection.
As for using it, why not either dive right in if the I/O is compatible (and it appears to be ok as is or minimally adaptable), or lift the parts of the schematic you like and can use. Use leds and switches to simulate what you are monitoring / controlling until there is minimal chance of releasing the magic component smoke.
Frank
yes, i was going to start with the digital i/o schematic and eventually just keep the components I would need. I think it would save time to start with that design and then step it down from there, vs. try and build it from scratch on my own.
After looking over the schematic I am sure the board will work with the propeller. It uses a '595 to drive a ULN2803, a combination often used with the propeller, and one I have used often in my own circuits. If circuit protection is an issue then I would consider either driving solid state relays directly from the propeller pins, driving mechanical relays by TPICs with the TPICs control signals going through optoisolators, or some combination of those two options.