I used a PicStart+ for quite a while when I started with Pics. When I moved to laptops, I suddenly lost my serial port. I bought something like this ( https://www.sparkfun.com/products/11304 ) from Sparkfun. It worked really well. I eventually bought Pics that it couldn’t program with the PicStart+ under Linux ( with picp ), so I bought a PicKit II from Mouser for about USD $30.00. It is USB and connects to the ICSP pins of the Pics ( MCLR, Vcc, Gnd, PGD, and PGC ). It works flawlessly on all my Pics. I haven’t upgraded to the PicKit III yet because I’m not sure if it will work under Linux. It might with MPLabX, but I haven’t checked. I see that Mouser now sells it for USD $34.99 here: http://www.mouser.com/ProductDetail/Microchip-Technology/PG164120/?qs=sGAEpiMZZMtdAabcSkQOl4ERF8GmpIKm
With the USB to serial converter, I had to do some work to get it to work under Linux. I needed to add a rule in /etc/udev/rules.d. It wasn’t too hard once I knew what to do. I’m not sure what it takes under Windows or Mac. Sparkfun includes a datasheet and driver downloads, though. Let me know if you have any questions.
Apologies. I thought you were looking for a way to get your chips programmed. If you are more interested in the building of your own, let’s see what we can find. I went to sparkfun.com and searched in the Breakouts section. There are several USB to Serial breakdout boards. Now, I know you want to build your own, and this is why I went to Sparkfun. They are very into OpenHardware, so they usually have schematics, datasheets, drivers, examples, etc. This is no exception. I grabbed a link for one that has a schematic: https://www.sparkfun.com/products/198
I was re-reading your initial question. I wonder if I understand what you are looking for? This is what I understand:
You want to build a circuit to program Pic microcontrollers. This programmer will have a USB plug to connect to a PC. It will have an output plug that will program the Pics with Low Voltage Programming ( as opposed to the normal ICSP style ). The PC programming software is set up to send the Hex file via PS232. You will adjust the PC to send the RS232 signal from the programming software over USB to the programmer. The programmer will have an onboard USB to serial converter like an FTDI. The converted RS2332 signal will be passed to an onboard microcontroller. This onboard controller will read in the Hex file. It will then send the LVP control signals to the chip that you wish to program. Is this correct?
If so, I couldn’t find a schematic that specifically covered LVP ( low voltage programming ). I belive you could use the converter schematic I pointed to for part of your design. You would wire the serial output from this to the microcontroller on your programmer. It will be up to you to generate the LVP programming commands on this controller. Microchip has Application Notes on how to do this. I’ve heard that LVP is pretty finicky and not too reliable, so I’ve always stuck with regular ICSP.
You can look around on sparkfun.com for more ideas. They have a pretty good forum as well. You might also try joing the piclist (http://piclist.org). There are many knowledgable engineers on that list. Good Luck!
my first programmer was a “jdm” type programmer that works perfectly with a real serial port. when I bought a new laptop (offcourse without a serial port) I bought an usb to serial cable… however this was not working at all. so I just want to warn you that not every programmer wil work with such an cable.
now I have an “galvawisp” that does have a pic in its own circuit to work, so an smarter kind of programmer. I’m using it together with the same usb to serial cable today and that just works great for me.
I understand now. Thanks. If you combine the converter I posted earlier with this circuit ( page has schematic download ) https://www.sparkfun.com/products/133 . I think that should do it. The circuit uses simple transistors in place of a Max232. It includes the signal inversion you are looking for. The circuit is very simple. I used to use an even simpler version when breadboarding, but I can’t find the link to the circuit. The one from sparkfun is more robust anyway.
The converter you posted earlier is correct but for what i want its not combined with the second i think.
One thing i was confused last days and one teacher explained to me,is that max232 is only for
serial communication and NOT programming.So you can’t send a hex file to program the pic.This i believed but it’s not.For programming the pic you don’t use max232.
In conclusion i need the usb to serial converter like the one you posted with cp2102 combined with a 74ls14n for example.Outputs of cp2102 connected to a hex inverter (74ls14n).
Thanks for all the help,i will try the schematic i posted (FT245BL and 74ls14) or another one the next days and i will post the result if it’s working.
Okay. If you have it worked out, that’s great. I’d love to hear what you come up with. I’m a bit confused why the inverter I posted won’t work. The converter lets you send RS232 signal over USB. The shifter board I posted takes the RS232 serial signal and inverts it ( the same, I think as the 74LS14 ) to TTL. If the output from the shifter goes directly to the RX and TX of your programmer’s microcontroller, it can read them perfectly with the built in AUSART peripheral. You can use the 74LS if you like; I thought the transistor solution might be faster, cheaper, and smaller footprint.
