Schematic Output Conflict Review

What it is for

Two push-pull outputs on one net fight each other: when one drives high and the other low, the result is an undefined level and, in real hardware, a large current through both output stages. Schematic Output Conflict Review looks for exactly this mistake in a saved Ohmforge project. Paste the contents of an exported .ohmforge.json file and it lists every pair of catalogued outputs that end up on the same net, whether through wires, a T-junction or matching net labels.

The check is deliberately narrow. It only knows pin roles for the built-in AND, OR, NAND, NOR, XOR and NOT gates and the comparator model. Every other pin (resistors, transistors, op-amps, supply pins of the comparator) is counted as unclassified and is never assumed to be safe. It does not check power, voltage compatibility, ratings, undriven inputs or anything on a physical board.

Worked example

Choose Review two connected outputs. The project has two inverters: U1's output Y sits at grid point 3, 0 and a wire runs from there to U2's output at 13, 4. The summary reads "1 classified output pair shares a net. Every component pin has a catalogued role." The table shows one row, U1.Y, U2.Y on net N002. All four pins (two inputs, two outputs) are classified, so nothing was skipped.

Now choose Review a gate and a comparator joined by a net label. There is no wire between the two parts: the NAND output U1.Y and the comparator output U2.OUT each carry a label named SIG, and labels with the same name connect. The tool reports one pair, U1.Y and U2.OUT on net SIG, and says "4 component pins are unclassified." Those four are the two resistor pins and the comparator's V+ and V− supply pins. The pair count is reliable for the classified pins only; the four others were not examined.

Review an empty schematic returns "No classified output pairs share a net." That is not a pass mark: there is simply nothing to check.

How to read the result

The coverage metrics come first: output pairs found, pairs shown, pairs omitted, classified pins and unclassified pins. Read the unclassified count before trusting a zero. A schematic built mostly from transistors can show no conflicts because almost nothing was classified.

Each table row names the two terminals as part.pin plus the net name. In the JSON result every terminal also carries its grid point, so a script can point to it. Three or more outputs on one net produce every pair: three outputs give three pairs. The list stops at 100 pairs, but the total and the omitted count always include all of them.

Tips and common mistakes

• Net names such as N002 are generated and may change after you edit the schematic; use the part and pin names to find the problem.
• Labels are compared exactly, so SIG and sig are separate nets. A ground symbol and labels named 0 or GND (in any letter case) all join the ground net.
• Wires that only cross in the middle do not connect. A wire end touching another wire does.
• In the Ohmforge workspace the same check appears under Connectivity review as Output conflict review, with a Show button for each of the two parts.
• Open-drain or tri-state outputs are not modelled; the built-in gates are push-pull only.

FAQ

Does no conflict mean my logic circuit is correct?

No. It means none of the classified outputs share a net. Check inputs, supplies, logic levels and timing separately, and simulate the circuit.

Why are op-amp outputs not checked?

Their pin roles are not in the catalogue yet, so they count as unclassified. The tool reports them rather than guessing.

Can I check a KiCad schematic?

No. The tool accepts Ohmforge project JSON only, up to 200 KB and 200 parts. Use KiCad's own electrical rules check for KiCad projects.