hardware design questions homebrew protoboard
rwgast_logicdesign
Posts: 1,464
I started a thread like this before but I don't think I asked the right questions so here it is again but way more specific.
ok so im designing my own prop protoboard. Im trying to make a small pcb which is basically a breakout board for the prop chip that includes a replacable crystal, eprom, programming interface and hopefully 1.3, 3.3, 5 and 12 volt power rails.
The idea is to make a testing platform that plugs into a breadboard or easily sockets into a pref board.
Im probably going to source my parts from digi-key (unless someone knows a better us source) becuase they have basically everything i need and there components arent as exspensive as the one sold on parallax, im ok with my voltage regulators only being good to 0c instead of -40c.
ok my first question which is about the serial interface to program the chip. I dont want to get a prop plug becuase i dont want to make a seperate order at digi key and here. My idea is to interface the to the chip via a db9 connector by basically connecting the 4 pins the chip needs for programming directly to the the db9 connector. then connecting the db9 connector to a usb to serial cable specificaly this one http://www.sabrent.com/category/cables/SBT-USC1M/ the reason i chose this cable is it is available localy for 12 bucks. My thought is that using a system provide more options in the end anyways becuase you get access to the full serial protocall. Am i wrong about this it seems like more people would be using this option since it provides alot more options for projects that can use the 5 other serial pins? Is this a slower method of transfer? I cant find any speed data on the cabale to compare to the prop plugs 3Mbaud rating. The biggest problem i see is this cable uses the prolific chipset not the ftmi, i know prolific works with ardino so it should be fine with the prop all these chips do the same thing, but there are no official linux drivers.
Second im an overclocker at heart i cant resist, every device i own gets clocked if it can, id clock my digi camera if it were possible. Anyways from what i read the protoboard will take a 6mhz crystal no problems. I would like a replacable cerystal system on my board, i know the protoboard does this. can someone explain to me how to add a replaceanle crystal system. I would use headers and jumper wires but thats not clean how do the parallax boards do this? what socket/parts cleanly accomplish this? Also someone told me that you need to lay out your board correcty for to support oc, is there examples of this somewhere? I would like to expermint with heatsinks good thermal paste and variable regulator to notch up the voltage, if there is a correct way to lay out for this other than the defualt schematics in the handbook id really like to see them. I dont understand why oc would require anything special than maybe giving the ic some breathing room.
Now if i dont have leds or or vga or anything like that i can still run programs on the chip and see output and stuff via the serial link?
Lastly can someone reccomend a compatible 512k eeprom chip from ditikey. i was told this is the biggest eprom the prop can handel hardware wise.
ok so im designing my own prop protoboard. Im trying to make a small pcb which is basically a breakout board for the prop chip that includes a replacable crystal, eprom, programming interface and hopefully 1.3, 3.3, 5 and 12 volt power rails.
The idea is to make a testing platform that plugs into a breadboard or easily sockets into a pref board.
Im probably going to source my parts from digi-key (unless someone knows a better us source) becuase they have basically everything i need and there components arent as exspensive as the one sold on parallax, im ok with my voltage regulators only being good to 0c instead of -40c.
ok my first question which is about the serial interface to program the chip. I dont want to get a prop plug becuase i dont want to make a seperate order at digi key and here. My idea is to interface the to the chip via a db9 connector by basically connecting the 4 pins the chip needs for programming directly to the the db9 connector. then connecting the db9 connector to a usb to serial cable specificaly this one http://www.sabrent.com/category/cables/SBT-USC1M/ the reason i chose this cable is it is available localy for 12 bucks. My thought is that using a system provide more options in the end anyways becuase you get access to the full serial protocall. Am i wrong about this it seems like more people would be using this option since it provides alot more options for projects that can use the 5 other serial pins? Is this a slower method of transfer? I cant find any speed data on the cabale to compare to the prop plugs 3Mbaud rating. The biggest problem i see is this cable uses the prolific chipset not the ftmi, i know prolific works with ardino so it should be fine with the prop all these chips do the same thing, but there are no official linux drivers.
Second im an overclocker at heart i cant resist, every device i own gets clocked if it can, id clock my digi camera if it were possible. Anyways from what i read the protoboard will take a 6mhz crystal no problems. I would like a replacable cerystal system on my board, i know the protoboard does this. can someone explain to me how to add a replaceanle crystal system. I would use headers and jumper wires but thats not clean how do the parallax boards do this? what socket/parts cleanly accomplish this? Also someone told me that you need to lay out your board correcty for to support oc, is there examples of this somewhere? I would like to expermint with heatsinks good thermal paste and variable regulator to notch up the voltage, if there is a correct way to lay out for this other than the defualt schematics in the handbook id really like to see them. I dont understand why oc would require anything special than maybe giving the ic some breathing room.
Now if i dont have leds or or vga or anything like that i can still run programs on the chip and see output and stuff via the serial link?
Lastly can someone reccomend a compatible 512k eeprom chip from ditikey. i was told this is the biggest eprom the prop can handel hardware wise.
Comments
There are a bunch of other items in your post I don't have time to reply to but I will let you know the Prop can also use 1024kbit EEPROM, you just have to address the upper 512 bits a bit differently than the lower 512 bits.
One of the many Propeller boards already available wont meet your needs? It just seems like there are a lot of Propeller board options these days.
Have you see the open source boards Tubular is having made? There might be something there that you could just tweak a bit.
I'll upload a picture of one of the boards I use with a breadboard here a little later (I'll edit this post). Maybe it will give you some more ideas of what you'd like. I'll also try to find the part numbers of the EEPROMs I get from Digi-Key. Do you want DIP chips? If so, the DIP choices have been decreasing lately.
Yeah, I can't figure out why the price is so different on those two chips. The less expensive chip has a greater operating voltage range. The 400khz speed is for voltages less than 2.5V. The more expensive chip doesn't operate below 2.5V so doesn't include the 400khz spec (at least this is my guess).
If I were buying 64K (DIP) EEPROMs from Digi-Key today, I'd by the $196 chip. I received an "end of life" notice from Digi-Key on the DIP EEPROMs I had previously purchased from them.
The Scribbler2 schematics have the circuit for the DB9 interface on page 9 (Back PCB Sheet 1). This should be everything you need.
1. I don't think many use RS232 these days. For safety, use an MAX3232. Don't forget you will need the transistor reset circuit! Alternately you could use the cheap usb cp2102 dongles (ttl) and put series resistors (you may not require them if the dongle operates at 3v3) and the transistor reset circuit on your pcb. The cp2102 are on eBay for about $4 shipped - and they will provide 5V provided you dont require a lot of current - beware, the 3v3 will likely not have enough current. Note however, you may need to add a wire to access the DTR pin (although you can use RTS) - it is quite tight to solder the wire to the chip on some of these dongles. While you can actually get away without the reset circuit in some circumstances, you will get resets when changing pc software without it. There are threads discussing this - I started one so do an advanced search. I have a tiny pcb for the FT232RL chip which I sell - its also on the open hardware pcb of tubular's.
2. Overclocking: There are many threads about this. For overclocking you need to adhere to professional design practices with extra capacitors. I regularly overclock using 6.5MHz (104MHz) and sometimes 13.5MHz*8 (108MHz). No need to worry about heatsinking the prop - it doesn't even get warm. I still use 3v3.
3. Xtal socket: I use IC pins from digikey. Not sure of the part no. They are also used on the Parallax ProtoBoards. You need .040" holes and the pins barely protrude above the pcb, so you dont really know they are there.
4. Eeprom: You require an AT24C256/512/1024 compatible. Some other eeproms have different programming page sizes and are not compatable. Most of us use 512Kb (64KB) but the prop only requires 32KB - but some use the extra space for things. I would rather add a microSD socket for more memory because it is faster. Digi has a good smt microSd with exposed pins at the front that I use.
5. Serial link: (usually via USB these days). The download speed is 115,200 baud. Yes, you can have your program write back to the PC as a 2way terminal. PropTool can invoke its own terminal (PST) after loading using F12. Put a few second delay in your program to allow you time to switch - you will get faster and can speed this up later.
Hope this helps.