Self-Made Prop-Plug only works sometimes...

bazi

I've made a serial programmer with a PL2303 chip for USB-RS232 conversion, a MAX3232 for levelshifting and and a BC547 transistor on the reset-line.

Schematics are easy, the PL2303 works fine, he could not be the problem. The MAX3232 is connected like this

The BC547 is connected like this:


Base ----| R=1K |

---

> serial DTR (pin 4)
Emmiter ----> GND
Collector ----> Reset

If i change E to C and C to E it works also, i'm wondering why, shouldn't there be a diode in a transistor?

Now the problem, if i press F7 (identify hardware) in the propeller tool, sometimes it works and sometimes he tells me, theres no propeller chip.

I'm very very new to the propeller, i even didn't some playing around with leds and the propeller etc. [noparse];)[/noparse]

Does anyone know what causes this (bad) behaviour?

Cluso99

Have you checked the propplug schematic? There is a cap in series from DTR to the base and a resistor from the base to emitter (IIRC about 20K).

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade,·RamBlade,·SixBlade, website
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
· Prop Tools under Development or Completed (Index)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)
· Search the Propeller forums·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm

bazi

Heres the schematic

You're right, theres a cap and a resistor. The resistor (10k) pulls the base down while the cap is loaded, while loading theres a high-pulse. I thought this would'nt be neccessary and i tried it on my breadboard with the cap and the pulldown and it was the same behaviour.

Cluso99

I am presuming you replaced the 2 transistors and associated resistors for the Rx & Tx inversion with the MAX3232 circuit ? I suggest you use 150R series resistors from the MAX3232 to RX & TX pins on the prop.

Looking at the circuit you posted the reset line will be triggered from the opposite DTR edge to what we normally use since we are using an inverted DTR. We don't have a series 10K with the cap either.

So, if it does not work with the cap then try taking the DTR via the MAX3232 and then into the cap and then to the base of the transistor. A 10K pull down should be fine but no 10K in series with the cap.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade,·RamBlade,·SixBlade, website
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
· Prop Tools under Development or Completed (Index)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)
· Search the Propeller forums·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz·· MultiBladeProp is: www.bluemagic.biz/cluso.htm

Toby Seckshund

@ Bazi

The three transistor cct is the one I use, I tried to be a bit more of a purist and did a MAX3232 (3 V version ) and the inverting transistor for ther resets.

The MAX cct will give true '232 voltages in and OUT, whereas the transistors rely on the volts supplied from the PC. The cct I copied for the MAX was from a thread about 9 months ago and stated the P30,P31 reversed (or I read it so ). I now put three jumpers on my interface two so that RX and TX can be swapped over, and a disconnect for the reset line so that comms won't cause resets when you dont want them.

As with the Elektor artical I copied, I use 5 wires GND, 3.3V, Rx, TX, and Reset.

PS I have just thought, sometimes I get "No prop found" for the first time of trying, cancell and try again and there it is, BST seems to find it always.

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Style and grace : Nil point

Post Edited (Toby Seckshund) : 12/27/2009 9:38:17 PM GMT

mikediv

Bazi I have home built a few myself even the 3 dollars usb cable posted in the completed project section I have had the exact same thing sometimes it works sometimes it does not but if I hit the key again most of the time it will connect, look at your signal with a scope I found for some reason sometime there is a small delay just enough to cause this problem I have tried caps and a resistor but to be honest with you sometimes it still happens the best performance I have gotten so far beside prop plug is putting a cap across dtr-gnd I wish I could tell you it would be a 100percent cure but its not , try it and see what happens for you
Oh I used a .22 mylar