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DonTronics - DT104

DT104 Atmel Micro on a Simmstick.

Download Schematic in PDF format.

I have been able to run a 1200 Micro in the DT104 Simmstick board with just the 20 pin Micro, a 16Mhz crystal and two caps either side or the crystal. C3 and C4. That's all you need for a minimal system. This means it can be built in what, 3 or 4 minutes?

Board Components:

This board was designed for Atmel AVR 20 pin DIP Micros, however it suits both AVR and non-AVR devices. Minor changes need to be made if you choose to use the DT104 with a non-AVR micro such as the AT89C2051. If you are using it with say the AT90S1200, then no changes are required and many components don't need to be installed.

1 by DT104 SimmStickTM PCB

1 by 780L5 +5 Voltage regulator in TO-92 case. (Optional)
1 by Capacitor C1 .01uf (or .1uf) Ceramic
1 by Capacitor C2 .01uf (or .1uf) Ceramic
1 by Capacitor C3 15pf to 30pf Ceramic (Install only if Crystal is installed)
1 by Capacitor C4 15pf to 30pf Ceramic (Install only if Crystal is installed)
1 by Capacitor C9 4.7uf Electrolytic (PCB mount.) or Tant. @16 V. (pwr-res)

For AVR devices:
At the time of writing, the capacitor values either side of the crystal
is yet to be determined, as no value is specified in the data sheets.

1 by Resistor  R1 10K .25 watt (Res pull-up and part of power-up reset).

1 by Resistor  R2 10K .25 watt (D0 pull-up only for non-AVR Micro.)
1 by Resistor  R3 10K .25 watt (D1 pull-up only for non-AVR Micro.)

1 by Resistor  R4 10K .25 watt (Install only if E3 EEPROM is installed)
1 by Resistor  R5 10K .25 watt (Install only if E3 EEPROM is installed)

1 by Resistor  R6 10K .25 watt (Install only for non-AVR.)
1 by Resistor  R7 10K .25 watt (Install only for non-AVR.)
1 by Resistor  R8 10K .25 watt (Used for power up-reset circuit.)                
1 by PNP small signal transistor. BC558. (Install only for non-AVR.)
US Type 2N4403 can be used, however it must be rotated 180 degrees so 
that the flat side of the transistor is facing away from R7 and not 
towards it as shown on the overlay.                

And either a Crystal of a suitable value, or a 3 pin Resonator. If a crystal is fitted then C3 and C4 must be installed. If you use a Resonator, then you mustn't install these two caps.
Again, at the time of writing, I don't think anyone has been able to get an AVR device to start with a Resonator.

The most common crystal used for beginners is 16Mhz, as this matches in with the AT90S1200-16PC that is currently the starting point for AVR devices.

Serial Communications:
1 by Capacitor C5 1uf Electrolytic (PCB mount.) or Tant. @16 V.
1 by Capacitor C6 1uf Electrolytic (PCB mount.) or Tant. @16 V.
1 by Capacitor C7 1uf Electrolytic (PCB mount.) or Tant. @16 V.
1 by Capacitor C8 1uf Electrolytic (PCB mount.) or Tant. @16 V.
1 by MAX-232 E2 (or equivalent)                

Brown-Out Circuit:
This small IC in a TO-92 package is used to stop the Micro operation becoming unpredictable during a power 'brown-out'. In most cases this isn't required. It's just an added precaution for reliable operation. The older Micros may well need this device.

By just simply ignoring the brown-out circuit and installing resistors R1, R8, and C9, the circuit operation should be fine.

If you wish to use the brown-out circuit, it's just added to the board, and can be either a CMOS or Open Collector type.
You can use the following I.C.'s:
Panasonic MN13811-S (Open Collector)
Panasonic MN1381-S (CMOS)
Zetek ZM33064
Motorola MC33064P
Other types may also be suitable. These should switch at between 4.2 and 4.6Volts. This is for +5 Volt operation.

It may also pay to install a 16 pin socket for the Max-232, as you may have to remove it for some configurations.


J1: +5Volt Isolation.
Used to Isolate the +5V signal on the edge connector from the 78L05 regulator output if it is installed. Both outputs should never be used together. The track on the solder side of the board under J1 needs to be cut to isolate the 78L05 regulator output. A test link and two male posts are used to reinstall the regulator output.

J2: AUX. Power In.
Brings in an alternative source of DC power. A 9 Volt battery may be connected to J2. Pin 1 is positive and pin 2 negative.

J3: RESET Inversion.
Controls the reset level required for the Micro. Needs to be reset low for AVR, then returned high, and high to reset returning to low for non-AVR.

For AVR operation, the board requires no alteration to this header. Components R7, Q1, and R6 are left out for AVR and installed for non-AVR. Also for non-AVR, the track needs to be cut on the solder side or the board between pins 1 and 2, and a wire link, or header pins and test link needs to be installed.

J4: Using the 104 as a Programmer.
The board is default set to be a standard target board. To make it into a programmer, the track must be changed much the same as described in the above J3 section, that is isolate pins 1 and 2, and connect pins 2 and 3  together.

J5: SPI Bus
The 20 pin AVR devices don't have an SPI bus, but software can be used to produce one, so this header was included. Also contains all the signals required for In-Circuit-Programming, so a cable with a DB-25 Male connector to an 8 pin SIL header can be used to program the device from a printer port. Check out the simple Jerry Meng programmer circuit. I had to add a 680pf cap between pin 19 of the Micro and ground to get Jerry's circuit to be reliable.

J6: Using the 104 as a Programmer.
Used for signal isolation when the DT104 is used as a programmer.

When used as a target board, the default board setting is correct. If used as a programmer, this link can be isolated, but it's not required unless you have I/O connected to D9 on the Simmstick bus and are concerned about the signal pulsing during the programming cycle.

The D9 signal has been renamed to XD9 after the link, meaning external to the bus, not the module. XD9 is used by the programming board to take control of the target board as it is jumpered via J4 to the target board reset signal.

Circuit diagram for DT104

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Last modified: February 24, 2016